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-<div class="header">\r
-<h1>Chess Engine Communication Protocol</h1>\r
-<h2><a href="http://www.tim-mann.org/">Tim Mann</a> & <a href="http://home.hccnet.nl/h.g.muller/winboardF.html">H.G.Muller</a></h2>\r
-<p>\r
-Version 2; implemented in xboard/WinBoard 4.2.1 and later. (Sept 3, 2009)<br />\r
-Changes since version 1 are indicated in <span class="version1">red</span>.<br />\r
-Changes for WinBoard 4.3.xx are indicated in <span class="version43">green</span>.<br />\r
-Changes for WinBoard 4.4.xx are indicated in <span class="version44">blue</span>.\r
-</p>\r
-</div>\r
-\r
-<ul>\r
-<li><a href="#1">1. Introduction</a></li>\r
-<li><a href="#2">2. Connection</a></li>\r
-<li><a href="#3">3. Debugging</a></li>\r
-<li><a href="#4">4. How it got this way</a></li>\r
-<li><a href="#5">5. WinBoard requires Win32 engines</a></li>\r
-<li><a href="#6">6. Hints on input/output</a></li>\r
-<li><a href="#7">7. Signals</a></li>\r
-<li><a href="#8">8. Commands from xboard to the engine</a></li>\r
-<li><a href="#9">9. Commands from the engine to xboard</a></li>\r
-<li><a href="#10">10. Thinking Output</a></li>\r
-<li><a href="#11">11. Time control</a></li>\r
-<li><a href="#12">12. Analyze Mode</a></li>\r
-<li><a href="#13">13. Idioms and backward compatibility features</a></li>\r
-</ul>\r
-\r
-<hr />\r
-\r
-<h2><a name="1">1. Introduction</a></h2>\r
-\r
-<p>\r
-This document is a set of rough notes on the protocol that xboard and\r
-WinBoard use to communicate with gnuchessx and other chess engines.\r
-These notes may be useful if you want to connect a different chess\r
-engine to xboard. Throughout the notes, "xboard" means both xboard\r
-and WinBoard except where they are specifically contrasted.\r
-</p>\r
-\r
-<p>\r
-There are two reasons I can imagine someone wanting to do this: \r
-</p>\r
-\r
-<ol>\r
-<li>You have, or are developing, a chess engine but you don't want to\r
-write your own graphical interface. </li>\r
-<li>You have, or are developing,a chess engine, and you want to\r
-interface it to the Internet Chess Server.</li>\r
-</ol>\r
-\r
-<p>\r
-In case (2), if you are using xboard, you will need to configure the\r
-"Zippy" code into it, but WinBoard includes this code already. See\r
-the file <a\r
-href="http://www.tim-mann.org/xboard/zippy.README">zippy.README</a>\r
-in the xboard or WinBoard distribution for more information.\r
-</p>\r
-\r
-<p>\r
-These notes are unpolished, but I've attempted to make them complete\r
-in this release. If you notice any errors, omissions, or misleading\r
-statements, let me know.\r
-</p>\r
-\r
-<p>\r
-I'd like to hear from everyone who is trying to interface their own\r
-chess engine to xboard/WinBoard. Please join the mailing list for \r
-authors of xboard/WinBoard compatible chess engines and post a message \r
-about what you're doing. The list is now hosted by Yahoo Groups; you \r
-can join at <a href="http://groups.yahoo.com/group/chess-engines" \r
->http://groups.yahoo.com/group/chess-engines</a>, or you can read the\r
-list there without joining. The list is filtered to prevent spam.\r
-</p>\r
-\r
-<p class="version43">\r
-Note that the WinBoard 4.3.xx line was developed independently of the\r
-original GNU project, by H.G.Muller.\r
-If you have questions about WinBoard 4.3.xx, or want to report bugs in it,\r
-report them in the appropriate section of the \r
-<a href="http://www.open-aurec.com/wbforum/">WinBoard forum</a>.\r
-</p>\r
-\r
-<h2><a name="2">2. Connection</a></h2>\r
-\r
-<p>\r
-An xboard chess engine runs as a separate process from xboard itself,\r
-connected to xboard through a pair of anonymous pipes. The engine\r
-does not have to do anything special to set up these pipes. xboard\r
-sets up the pipes itself and starts the engine with one pipe as its\r
-standard input and the other as its standard output. The engine then\r
-reads commands from its standard input and writes responses to its\r
-standard output. This is, unfortunately, a little more complicated to\r
-do right than it sounds; see <a href="#6">section 6</a> below.\r
-</p>\r
-\r
-<p>\r
-And yes, contrary to some people's expectations, exactly the same\r
-thing is true for WinBoard. Pipes and standard input/output are\r
-implemented in Win32 and work fine. You don't have to use DDE, COM,\r
-DLLs, BSOD, or any of the other infinite complexity that\r
-Microsoft has created just to talk between two programs. A WinBoard\r
-chess engine is a Win32 console program that simply reads from its\r
-standard input and writes to its standard output. See sections \r
-<a href="#5">5</a> and <a href="#6">6</a> below for additional details.\r
-</p>\r
-\r
-<h2><a name="3">3. Debugging</a></h2>\r
-\r
-<p>\r
-To diagnose problems in your engine's interaction with xboard, use the\r
--debug flag on xboard's command line to see the messages that are\r
-being exchanged. In WinBoard, these messages are written to the file\r
-WinBoard.debug instead of going to the screen.\r
-</p>\r
-\r
-<p>\r
-You can turn debug mode on or off while WinBoard is running by\r
-pressing Ctrl+Alt+F12. You can turn debug mode on or off while xboard\r
-is running by binding DebugProc to a shortcut key (and pressing the\r
-key!); see the instructions on shortcut keys in the xboard man page.\r
-</p>\r
-\r
-<p>\r
-While your engine is running under xboard/WinBoard, you can send a\r
-command directly to the engine by pressing Shift+1 (xboard) or Alt+1\r
-(WinBoard 4.0.3 and later). This brings up a dialog that you can type\r
-your command into. Press Shift+2 (Alt+2) instead to send to the\r
-second chess engine in Two Machines mode. On WinBoard 4.0.2 and earlier,\r
-Ctrl+Alt is used in place of Alt; this had to be changed due to a conflict\r
-with typing the @-sign on some European keyboards.\r
-</p>\r
-\r
-<h2><a name="4">4. How it got this way</a></h2>\r
-\r
-<p>\r
-Originally, xboard was just trying to talk to the existing\r
-command-line interface of GNU Chess 3.1+ and 4, which was designed\r
-for people to type commands to. So the communication protocol is very\r
-ad-hoc. It might have been good to redesign it early on, but because\r
-xboard and GNU Chess are separate programs, I didn't want to force\r
-people to upgrade them together to versions that matched. I\r
-particularly wanted to keep new versions of xboard working with old\r
-versions of GNU Chess, to make it easier to compare the play of old\r
-and new gnuchess versions. I didn't foresee the need for a clean\r
-protocol to be used with other chess engines in the future.\r
-</p>\r
-\r
-<p>\r
-Circumstances have changed over the years, and now there are many more\r
-engines that work with xboard. I've had to make the protocol\r
-description more precise, I've added some features that GNU Chess\r
-does not support, and I've specified the standard semantics of a few\r
-features to be slightly different from what GNU Chess 4 does.\r
-</p>\r
-\r
-<p class="version1">\r
-This release of the protocol specification is the first to carry a\r
-version number of its own -- version 2. Previous releases simply\r
-carried a last-modified date and were loosely tied to specific \r
-releases of xboard and WinBoard. The version number "1" applies\r
-generally to all those older versions of the protocol.\r
-</p>\r
-\r
-<p class="version1">\r
-Protocol version 2 remains compatible with older engines but has\r
-several new capabilities. In particular, it adds the \r
-"feature" command, a new mechanism for making backward-compatible\r
-changes and extensions to the protocol. Engines that do not support a\r
-particular new feature do not have to use it; new features are not\r
-enabled unless the engine specifically requests them using the feature\r
-command. If an engine does not send the feature command at all, the\r
-protocol behavior is nearly identical to version 1. Several new\r
-features can be selected by the feature command in version 2,\r
-including the "ping" command (recommended for all engines), the\r
-"setboard" command, and many optional parameters. Additional features\r
-will probably be added in future versions.\r
-</p>\r
-\r
-<p class="version43">\r
-If it is necessary to have a separate name, \r
-it would be best to refer to the protocol including the green additions as version 2f.\r
-I really don't think it is a different protocol from version 2, though.\r
-I just tried to clarify some ambiguities in the original definition,\r
-now that the WinBoard 4.3.xx line has implemented them in a specific way.\r
-The hand-shaking protocol for features as defined in protocol 2 perfectly\r
-allows addition of an occasional new features without any need for stepping up the protocol version number,\r
-and I think refraining from the latter would enormously lower the barrier for actual\r
-implementation of these features in engines.\r
-<br />\r
-The two really new things are the engine debug comments, and the "nps" command.\r
-The former merely tries to regulate an extremely common existing pactice \r
-of having engines dump debug messages on WinBoard in an unprotected way, \r
-as usually you get away with that.\r
-</p>\r
-\r
-<h2><a name="5">5. WinBoard requires Win32 engines</a></h2>\r
-\r
-<p>\r
-Due to some Microsoft brain damage that I don't understand, WinBoard\r
-does not work with chess engines that were compiled to use a DOS\r
-extender for 32-bit addressing. (Probably not with 16-bit DOS or\r
-Windows programs either.) WinBoard works only with engines that are\r
-compiled for the Win32 API. You can get a free compiler that targets\r
-the Win32 API from <a href="http://sources.redhat.com/cygwin/"\r
->http://sources.redhat.com/cygwin/</a>. I think DJGPP 2.x should also\r
-work if you use the RSXNTDJ extension, but I haven't tried it. Of\r
-course, Microsoft Visual C++ will work. Most likely the other\r
-commercial products that support Win32 will work too (Borland, etc.),\r
-but I have not tried them. Delphi has been successfully used to write\r
-engines for WinBoard; if you want to do this, Tony Werten has donated\r
-some <a href="http://www.tim-mann.org/winboard/delphi.txt" >sample\r
-code</a> that should help you get started.\r
-</p>\r
-\r
-<h2><a name="6">6. Hints on input/output</a></h2>\r
-\r
-<p>\r
-Beware of using buffered I/O in your chess engine. The C stdio\r
-library, C++ streams, and the I/O packages in most other languages use\r
-buffering both on input and output. That means two things. First,\r
-when your engine tries to write some characters to xboard, the library\r
-stashes them in an internal buffer and does not actually write them to\r
-the pipe connected to xboard until either the buffer fills up or you\r
-call a special library routine asking for it to be flushed. (In C\r
-stdio, this routine is named <tt>fflush</tt>.) Second, when your engine tries\r
-to read some characters from xboard, the library does not read just\r
-the characters you asked for -- it reads all the characters that are\r
-currently available (up to some limit) and stashes any characters you\r
-are not yet ready for in an internal buffer. The next time you ask to\r
-read, you get the characters from the buffer (if any) before the\r
-library tries to read more data from the actual pipe.\r
-</p>\r
-\r
-<p>\r
-Why does this cause problems? First, on the output side, remember\r
-that your engine produces output in small quantities (say, a few\r
-characters for a move, or a line or two giving the current analysis),\r
-and that data always needs to be delivered to xboard/WinBoard for\r
-display immediately. If you use buffered output, the data you print\r
-will sit in a buffer in your own address space instead of being\r
-delivered.\r
-</p>\r
-\r
-<p>\r
-You can usually fix the output buffering problem by asking for the\r
-buffering to be turned off. In C stdio, you do this by calling\r
-<tt>setbuf(stdout, NULL)</tt>. A more laborious and error-prone\r
-method is to carefully call <tt>fflush(stdout)</tt> after every line\r
-you output; I don't recommend this. In C++, you can try\r
-<tt>cout.setf(ios::unitbuf)</tt>, which is documented in current\r
-editions of "The C++ Programming Language," but not older ones.\r
-Another C++ method that might work is\r
-<tt>cout.rdbuf()->setbuf(NULL, 0)</tt>. Alternatively, you can\r
-carefully call <tt>cout.flush()</tt> after every line you output;\r
-again, I don't recommend this.\r
-</p>\r
-\r
-<p>\r
-Another way to fix the problem is to use unbuffered operating system\r
-calls to write directly to the file descriptor for standard output.\r
-On Unix, this means <tt>write(1, ...)</tt> -- see the man page for write(2).\r
-On Win32, you can use either the Unix-like <tt>_write(1, ...)</tt> or Win32\r
-native routines like <tt>WriteFile</tt>.\r
-</p>\r
-\r
-<p>\r
-Second, on the input side, you are likely to want to poll during your\r
-search and stop it if new input has come in. If you implement\r
-pondering, you'll need this so that pondering stops when the user\r
-makes a move. You should also poll during normal thinking on your\r
-move, so that you can implement the "?" (move now) command, and so\r
-that you can respond promptly to a "result", "force", or "quit"\r
-command if xboard wants to end the game or terminate your engine.\r
-Buffered input makes polling more complicated -- when you poll, you\r
-must stop your search if there are <em>either</em> characters in the buffer\r
-<em>or</em> characters available from the underlying file descriptor.\r
-</p>\r
-\r
-<p>\r
-The most direct way to fix this problem is to use unbuffered operating\r
-system calls to read (and poll) the underlying file descriptor\r
-directly. On Unix, use <tt>read(0, ...)</tt> to read from standard input, and\r
-use <tt>select()</tt> to poll it. See the man pages read(2) and select(2).\r
-(Don't follow the example of GNU Chess 4 and use the FIONREAD ioctl to\r
-poll for input. It is not very portable; that is, it does not exist\r
-on all versions of Unix, and is broken on some that do have it.) On\r
-Win32, you can use either the Unix-like <tt>_read(0, ...)</tt> or the native\r
-Win32 <tt>ReadFile()</tt> to read. Unfortunately, under Win32, the function to\r
-use for polling is different depending on whether the input device is\r
-a pipe, a console, or something else. (More Microsoft brain damage\r
-here -- did they never hear of device independence?) For pipes, you\r
-can use <tt>PeekNamedPipe</tt> to poll (even when the pipe is unnamed).\r
-For consoles, \r
-you can use <tt>GetNumberOfConsoleInputEvents</tt>. For sockets only, you can\r
-use <tt>select()</tt>. It might be possible to use\r
-<tt>WaitForSingleObject</tt> more \r
-generally, but I have not tried it. Some code to do these things can\r
-be found in Crafty's utility.c, but I don't guarantee that it's all\r
-correct or optimal.\r
-</p>\r
-\r
-<p>\r
-A second way to fix the problem might be to ask your I/O library not\r
-to buffer on input. It should then be safe to poll the underlying\r
-file descriptor as described above. With C, you can try calling\r
-<tt>setbuf(stdin, NULL)</tt>. However, I have never tried this. Also, there\r
-could be problems if you use <tt>scanf()</tt>, at least with certain patterns,\r
-because <tt>scanf()</tt> sometimes needs to read one extra character and "push\r
-it back" into the buffer; hence, there is a one-character pushback\r
-buffer even if you asked for stdio to be unbuffered. With C++, you\r
-can try <tt>cin.rdbuf()->setbuf(NULL, 0)</tt>, but again, I have never tried\r
-this.\r
-</p>\r
-\r
-<p>\r
-A third way to fix the problem is to check whether there are\r
-characters in the buffer whenever you poll. C I/O libraries generally\r
-do not provide any portable way to do this. Under C++, you can use\r
-<tt>cin.rdbuf()->in_avail()</tt>. This method has been reported to\r
-work with \r
-EXchess. Remember that if there are no characters in the buffer, you\r
-still have to poll the underlying file descriptor too, using the\r
-method described above.\r
-</p>\r
-\r
-<p>\r
-A fourth way to fix the problem is to use a separate thread to read\r
-from stdin. This way works well if you are familiar with thread\r
-programming. This thread can be blocked waiting for input to come in\r
-at all times, while the main thread of your engine does its thinking.\r
-When input arrives, you have the thread put the input into a buffer\r
-and set a flag in a global variable. Your search routine then\r
-periodically tests the global variable to see if there is input to\r
-process, and stops if there is. WinBoard and my Win32 ports of ICC\r
-timestamp and FICS timeseal use threads to handle multiple input\r
-sources.\r
-</p>\r
-\r
-<h2><a name="7">7. Signals</a></h2>\r
-\r
-<p>Engines that run on Unix need to be concerned with two Unix\r
-signals: <tt>SIGTERM</tt> and <tt>SIGINT</tt>. This applies both to\r
-engines that run under xboard and (the unusual case of) engines that\r
-WinBoard remotely runs on a Unix host using the -firstHost or\r
--secondHost feature. It does not apply to engines that run on\r
-Windows, because Windows does not have Unix-style signals.\r
-<span class="version1">\r
-Beginning with version 2, you can now turn off the use of\r
-either or both\r
-signals. See the "feature" command in <a href="#6">section 9</a> below.\r
-</span>\r
-</p>\r
-\r
-<p>First, when an engine is sent the "quit" command, it is also given\r
-a <tt>SIGTERM</tt> signal shortly afterward to make sure it goes away.\r
-If your engine reliably responds to "quit", and the signal causes\r
-problems for you, you should either ignore it by calling\r
-<tt>signal(SIGTERM, SIG_IGN)</tt> at the start of your program,\r
-or disable it with the "feature" command.</p>\r
-\r
-<p>Second, xboard will send an interrupt signal (<tt>SIGINT</tt>) at\r
-certain times when it believes the engine may not be listening to user\r
-input (thinking or pondering). WinBoard currently does this only when\r
-the engine is running remotely using the -firstHost or -secondHost\r
-feature, not when it is running locally. You probably need to know\r
-only enough about this grungy feature to keep it from getting in your\r
-way.\r
-</p>\r
-\r
-<p>\r
-The <tt>SIGINT</tt>s are basically tailored to the needs of GNU Chess 4\r
-on systems where its input polling code is broken or disabled.\r
-Because they work in a rather peculiar way, it is recommended that you\r
-either ignore <tt>SIGINT</tt> by having your engine call\r
-<tt>signal(SIGINT, SIG_IGN)</tt>, or disable it with the "feature"\r
-command.</p>\r
-\r
-<p>\r
-Here are details for the curious. If xboard needs to send a command\r
-when it is the chess engine's move (such as before the "?" command), \r
-it sends a <tt>SIGINT</tt> first. If xboard needs to send commands when it is\r
-not the chess engine's move, but the chess engine may be pondering\r
-(thinking on its opponent's time) or analyzing (analysis or analyze\r
-file mode), xboard sends a <tt>SIGINT</tt> before the first such command only.\r
-Another <tt>SIGINT</tt> is not sent until another move is made, even if xboard\r
-issues more commands. This behavior is necessary for GNU Chess 4. The\r
-first <tt>SIGINT</tt> stops it from pondering until the next move, but on some\r
-systems, GNU Chess 4 will die if it receives a <tt>SIGINT</tt> when not \r
-actually thinking or pondering.\r
-</p>\r
-\r
-<p>\r
-There are two reasons why WinBoard does not send the Win32 equivalent\r
-of <tt>SIGINT</tt> (which is called <tt>CTRL_C_EVENT</tt>) to local\r
-engines. First, the Win32 GNU Chess 4 port does not need it. Second, I\r
-could not find a way to get it to work. Win32 seems to be designed\r
-under the assumption that only console applications, not windowed\r
-applications, would ever want to send a <tt>CTRL_C_EVENT</tt>.\r
-</p>\r
-\r
-<h2><a name="8">8. Commands from xboard to the engine</a></h2>\r
-\r
-<p>\r
-All commands from xboard to the engine end with a newline (\n), even\r
-where that is not explicitly stated. All your output to xboard must\r
-be in complete lines; any form of prompt or partial line will cause\r
-problems.\r
-</p>\r
-\r
-<p>\r
-At the beginning of each game, xboard sends an initialization string.\r
-This is currently "new\nrandom\n" unless the user changes it with the\r
-initString or secondInitString option.\r
-</p>\r
-\r
-<p>\r
-xboard normally reuses the same chess engine process for multiple\r
-games. At the end of a game, xboard will send the "force" command\r
-(see below) to make sure your engine stops thinking about the current\r
-position. It will later send the initString again to start a new\r
-game. If your engine can't play multiple games, you can disable reuse\r
-<span class="version1">\r
-either with the "feature" command (beginning in protocol version\r
-2; see below) or \r
-</span>\r
-with xboard's -xreuse (or -xreuse2) command line\r
-option. xboard will then ask the process to quit after each game and\r
-start a new process for the next game.\r
-</p>\r
-\r
-<dl>\r
-<dt>xboard</dt>\r
-<dd>This command will be sent once immediately after your engine\r
-process is started. You can use it to put your engine into "xboard\r
-mode" if that is needed. If your engine prints a prompt to ask for\r
-user input, you must turn off the prompt and output a newline when the\r
-"xboard" command comes in.\r
-</dd>\r
-\r
-<dt class="version1">protover N</dt>\r
-<dd class="version1">\r
-<p>Beginning in protocol version 2 (in which N=2), this command will\r
-be sent immediately after the "xboard" command. If you receive some\r
-other command immediately after "xboard" (such as "new"), you can\r
-assume that protocol version 1 is in use. The "protover" command is\r
-the only new command that xboard always sends in version 2. All other\r
-new commands to the engine are sent only if the engine first enables\r
-them with the "feature" command. Protocol versions will always be\r
-simple integers so that they can easily be compared.\r
-</p>\r
-\r
-<p>Your engine should reply to the protover command by sending the\r
-"feature" command (see below) with the list of non-default feature\r
-settings that you require, if any.</p>\r
-\r
-<p>Your engine should never refuse to run due to receiving a higher\r
-protocol version number than it is expecting! New protocol versions\r
-will always be compatible with older ones by default; the larger\r
-version number is simply a hint that additional "feature" command\r
-options added in later protocol versions may be accepted.\r
-</p>\r
-</dd>\r
-\r
-<dt class="version1">accepted</dt>\r
-<dt class="version1">rejected</dt>\r
-<dd class="version1">\r
-These commands may be sent to your engine in reply to the "feature"\r
-command; see its documentation below.\r
-</dd>\r
-\r
-<dt>new</dt>\r
-<dd>Reset the board to the standard chess starting position. Set\r
-White on move. Leave force mode and set the engine to play Black.\r
-Associate the engine's clock with Black and the opponent's clock with\r
-White. Reset clocks and time controls to the start of a new game.\r
-Use wall clock for time measurement.\r
-Stop clocks. Do not ponder on this move, even if pondering is on.\r
-Remove any search depth limit previously set by the sd command.\r
-</dd>\r
-\r
-<dt>variant VARNAME</dt>\r
-<dd>If the game is not standard chess, but a variant, this command is\r
-sent after "new" and before the first move or "edit" command. Currently\r
-defined variant names are:\r
-\r
-<table>\r
-<tr><td>wildcastle</td><td>Shuffle chess where king can castle from d file</td></tr>\r
-<tr><td>nocastle</td><td>Shuffle chess with no castling at all</td></tr>\r
-<tr><td>fischerandom</td><td>Fischer Random</td></tr>\r
-<tr><td>bughouse</td><td>Bughouse, ICC/FICS rules</td></tr>\r
-<tr><td>crazyhouse</td><td>Crazyhouse, ICC/FICS rules</td></tr>\r
-<tr><td>losers</td><td>Win by losing all pieces or getting mated (ICC)</td></tr>\r
-<tr><td>suicide</td><td>Win by losing all pieces including king,\r
- or by having fewer pieces when one player has no legal moves (FICS)</td></tr>\r
-<tr class="version1"><td>giveaway</td><td>Win by losing all pieces including king,\r
- or by having no legal moves (ICC)</td></tr>\r
-<tr><td>twokings</td><td>Weird ICC wild 9</td></tr>\r
-<tr><td>kriegspiel</td><td>Kriegspiel (engines not supported)</td></tr>\r
-<tr><td>atomic</td><td>Atomic</td></tr>\r
-<tr><td>3check</td><td>Win by giving check 3 times</td></tr>\r
-<tr class="version43"><td>xiangqi </td><td>Chinese Chess (9x10 board)</td></tr>\r
-<tr class="version43"><td>shogi </td><td>Japanese Chess (9x9 bord)</td></tr>\r
-<tr class="version43"><td>capablanca</td><td>Capablanca Chess (10x8 board, with Archbishop and Chancellor)</td></tr>\r
-<tr class="version43"><td>gothic </td><td>Gothic Chess (10x8 board, same with better opening setup)</td></tr>\r
-<tr class="version43"><td>falcon </td><td>Falcon Chess (10x8 board, with two Falcon pieces)</td></tr>\r
-<tr class="version43"><td>shatranj </td><td>ancient Arabic Chess, with Elephants and General in stead of B and Q</td></tr>\r
-<tr class="version43"><td>courier </td><td>Courier Chess (12x8 board, a medieval precursor of modern Chess</td></tr>\r
-<tr class="version43"><td>knightmate </td><td>King moves as Knight and vice versa</td></tr>\r
-<tr class="version43"><td>berolina</td><td> Pawns capture straight ahead, and move diagonally</td></tr>\r
-<tr class="version43"><td>janus</td><td> Janus Chess (10x8, with two Archbishops)</td></tr>\r
-<tr class="version43"><td>caparandom </td><td>shuffle variant like FRC (10x8 board)</td></tr>\r
-<tr class="version43"><td>cylinder </td><td>Pieces wrap around between side edges, like board is a cylinder</td></tr>\r
-<tr class="version44"><td>super </td><td>Superchess: a shuffle variant with 4 fairy pieces on 8x8 board</td></tr>\r
-<tr class="version44"><td>great </td><td>Great Shatranj: sliders are replaced by corresponding short-range pieces on a 10x8 board</td></tr>\r
-<tr><td>unknown</td><td>Unknown variant (not supported)</td></tr>\r
-</table>\r
-\r
-</dd>\r
-\r
-<dt>quit</dt>\r
-<dd>The chess engine should immediately exit. This command is used\r
-when xboard is itself exiting, and also between games if the -xreuse\r
-command line option is given (or -xreuse2 for the second engine).\r
-See also <a href="#7">Signals</a> above.\r
-</dd>\r
-\r
-<dt>random</dt>\r
-<dd>This command is specific to GNU Chess 4. You can either ignore it\r
-completely (that is, treat it as a no-op) or implement it as GNU Chess\r
-does. The command toggles "random" mode (that is, it sets random =\r
-!random). In random mode, the engine adds a small random value to its\r
-evaluation function to vary its play. The "new" command sets random\r
-mode off.\r
-</dd>\r
-\r
-<dt>force</dt>\r
-<dd>Set the engine to play neither color ("force mode"). Stop clocks.\r
-The engine should check that moves received in force mode are legal\r
-and made in the proper turn, but should not think, ponder, or make\r
-moves of its own.\r
-</dd>\r
-\r
-<dt>go</dt>\r
-<dd>Leave force mode and set the engine to play the color that is on\r
-move. Associate the engine's clock with the color that is on move,\r
-the opponent's clock with the color that is not on move. Start the engine's\r
-clock. Start thinking and eventually make a move.\r
-</dd>\r
-\r
-<dt class="version1">playother</dt>\r
-<dd class="version1">\r
-(This command is new in protocol version 2. It is not\r
-sent unless you enable it with the feature command.)\r
-Leave force mode and set the engine to play the color that is <i>not</i> on\r
-move. Associate the opponent's clock with the color that is on move,\r
-the engine's clock with the color that is not on move. Start the opponent's\r
-clock. If pondering is enabled, the engine should begin pondering.\r
-If the engine later receives a move, it should start thinking and eventually\r
-reply.\r
-</dd>\r
-\r
-<dt>white</dt>\r
-<dd>\r
-<p><span class="version1">\r
-(This command is obsolete as of protocol version 2, but is still\r
-sent in some situations to accommodate older engines unless you disable it \r
-with the feature command.)\r
-</span>\r
-Set White on move. Set the engine to play Black. Stop clocks.\r
-</p>\r
-</dd>\r
- \r
-<dt>black </dt>\r
-<dd>\r
-<span class="version1">\r
-(This command is obsolete as of protocol version 2, but is still\r
-sent in some situations to accommodate older engines unless you disable it \r
-with the feature command.)\r
-</span>\r
-Set Black on move. Set the engine to play White. Stop clocks.\r
-</dd>\r
-\r
-<dt>level MPS BASE INC</dt>\r
-<dd>Set time controls. See the <a href="#11">Time Control</a> section below.\r
-</dd>\r
- \r
-<dt>st TIME</dt>\r
-<dd>Set time controls. See the <a href="#11">Time Control</a> section\r
-below. \r
-</dd>\r
-\r
-<dt>sd DEPTH</dt>\r
-<dd>\r
-<p>The engine should limit its thinking to DEPTH ply.\r
-<span class="version43">The commands "level" or "st" and "sd" can be used together in an orthogonal way.\r
-If both are issued, the engine should observe both limitations:</span>\r
-In the protocol, the "sd" command isn't a time control. It doesn't\r
-say that your engine has unlimited time but must search to exactly the\r
-given depth. It says that you should pay attention to the time\r
-control as normal, but cut off the search at the specified depth even\r
-if you have time to search deeper. If you don't have time to search\r
-to the specified depth, given your normal time management algorithm,\r
-then you will want to stop sooner than the given depth.\r
-</p><p>\r
-The "new" command should set the search depth back to unlimited. This\r
-is already stated in the spec. The "level" command should not affect\r
-the search depth. As it happens, xboard/WinBoard currently always\r
-sends sd (if needed) right after level, but that isn't part of the\r
-spec.</p>\r
-</dd>\r
-\r
-<dt><span class="version43">nps NODE_RATE</span></dt>\r
-<dd><span class="version43">The engine should not use wall-clock time to make its timing decisions,\r
-but an own internal time measure based on the number of nodes it has searched\r
-(and will report as "thinking output", see <a href="#10">section 10</a>),\r
-converted to seconds through dividing by the given NODE_RATE.\r
-Example: after receiving the commands "st 8" and "nps 10000",\r
-the engine should never use more that 80,000 nodes in the search for any move.\r
-In this mode, the engine should report user CPU time used (in its thinking output), \r
-rather than wall-clock time.\r
-This even holds if NODE_RATE is given as 0,\r
-but in that case it should also use the user CPU time for its timing decisions.\r
-The effect of an "nps" command should persist until the next "new" command.\r
-</span>\r
-</dd>\r
-\r
-<dt>time N</dt>\r
-<dd>Set a clock that always belongs to the engine. N is a number in\r
- centiseconds (units of 1/100 second). Even if the engine changes to\r
- playing the opposite color, this clock remains with the engine.\r
-</dd>\r
-\r
-<dt>otim N</dt>\r
-\r
-<dd><p>Set a clock that always belongs to the opponent. N is a number in\r
-centiseconds (units of 1/100 second). Even if the opponent changes to\r
-playing the opposite color, this clock remains with the opponent.\r
-</p><p>\r
-If needed for purposes of board display in force mode (where the\r
-engine is not participating in the game) the time clock should be\r
-associated with the last color that the engine was set to play, the\r
-otim clock with the opposite color.\r
-</p>\r
-<p>\r
-<span class="version43">This business of "clocks remaining with the engine" is apparently so ambiguous\r
-that many engines implement it wrong.\r
-The clocks in fact always remain with the color.\r
-Which clock reading is relayed with "time", and which by "otim", is determined by which side the engine plays.\r
-Note that the way the clocks operate and receive extra time (in accordance with the selected time control)\r
-is not affected in any way by which moves are made by the engine, which by the opponent, and which were forced.\r
-</span>\r
-</p>\r
-<p>\r
-<span class="version1">\r
-Beginning in protocol version 2, if you can't handle the time and\r
-otim commands, you can use the "feature" command to disable them; see\r
-below. \r
-</span>\r
-The following techniques from older protocol versions also\r
-work: You can ignore the time and otim commands (that is, treat them\r
-as no-ops), or send back "Error (unknown command): time" the first\r
-time you see "time".\r
-</p></dd>\r
-\r
-<dt>MOVE</dt>\r
-<dd>\r
-<p>See below for the syntax of moves. If the move is illegal, print\r
-an error message; see the section "<a href="#9">Commands from the engine to\r
-xboard</a>". If the move is legal and in turn, make it. If not in force\r
-mode, stop the opponent's clock, start the engine's clock, start\r
-thinking, and eventually make a move.\r
-</p><p>\r
-When xboard sends your engine a move, it normally sends coordinate\r
-algebraic notation. Examples:\r
-</p>\r
-<table>\r
-<tr><td>Normal moves:</td><td>e2e4</td></tr>\r
-<tr><td>Pawn promotion:</td><td>e7e8q</td></tr>\r
-<tr><td>Castling:</td><td>e1g1, e1c1, e8g8, e8c8</td></tr>\r
-<tr><td>Bughouse/crazyhouse drop:</td><td>P@h3</td></tr>\r
-<tr><td>ICS Wild 0/1 castling:</td><td>d1f1, d1b1, d8f8, d8b8</td></tr>\r
-<tr><td>FischerRandom castling:</td><td>O-O, O-O-O (oh, not zero)</td></tr>\r
-</table>\r
-\r
-<p class="version43">\r
-Note that on boards with more than 9 ranks, counting of the ranks starts at 0.\r
-</p>\r
-<p class="version1">\r
-Beginning in protocol version 2, you can use the feature command\r
-to select SAN (standard algebraic notation) instead; for example, e4,\r
-Nf3, exd5, Bxf7+, Qxf7#, e8=Q, O-O, or P@h3. Note that the last form,\r
-P@h3, is a extension to the PGN standard's definition of SAN, which does\r
-not support bughouse or crazyhouse.\r
-</p>\r
-\r
-<p>\r
-xboard doesn't reliably detect illegal moves, because it does not keep\r
-track of castling unavailability due to king or rook moves, or en\r
-passant availability. If xboard sends an illegal move, send back an\r
-error message so that xboard can retract it and inform the user; see\r
-the section "<a href="#9">Commands from the engine to xboard</a>".\r
-</p>\r
-</dd>\r
-<dt class="version1">usermove MOVE</dt>\r
-<dd class="version1">\r
-By default, moves are sent to the engine without a command name;\r
-the notation is just sent as a line by itself.\r
-Beginning in protocol version 2, you can use the feature command\r
-to cause the command name "usermove" to be sent before the move.\r
-Example: "usermove e2e4".\r
-</dd>\r
-\r
-<dt>?</dt>\r
-<dd><p>Move now. If your engine is thinking, it should move immediately;\r
- otherwise, the command should be ignored (treated as a no-op). It\r
- is permissible for your engine to always ignore the ? command. The\r
- only bad consequence is that xboard's Move Now menu command will do\r
- nothing.\r
-</p><p>\r
-It is also permissible for your engine to move immediately if it gets\r
-any command while thinking, as long as it processes the command right\r
-after moving, but it's preferable if you don't do this. For example,\r
-xboard may send post, nopost, easy, hard, force, quit,\r
-<span class="version1">\r
-or other commands\r
-</span>\r
-while the engine is on move.\r
-</p>\r
-</dd>\r
-\r
-<dt class="version1">ping N</dt>\r
-<dd class="version1">\r
-<p>In this command, N is a decimal number. When you receive the command,\r
-reply by sending the string <strong>pong N</strong>, where N is the\r
-same number you received. Important: You must not reply to a "ping"\r
-command until you have finished executing all commands that you\r
-received before it. Pondering does not count; if you receive a ping\r
-while pondering, you should reply immediately and continue pondering.\r
-Because of the way xboard uses the ping command, if you implement the\r
-other commands in this protocol, you should never see a "ping" command\r
-when it is your move; however, if you do, you must not send the "pong"\r
-reply to xboard until after you send your move. For example, xboard\r
-may send "?" immediately followed by "ping". If you implement the "?"\r
-command, you will have moved by the time you see the subsequent ping\r
-command. Similarly, xboard may send a sequence like "force", "new",\r
-"ping". You must not send the pong response until after you have\r
-finished executing the "new" command and are ready for the new game to\r
-start.\r
-</p>\r
-<p>\r
-The ping command is new in protocol version 2 and will not be sent\r
-unless you enable it with the "feature" command. Its purpose is to\r
-allow several race conditions that could occur in previous versions of\r
-the protocol to be fixed, so it is highly recommended that you\r
-implement it. It is especially important in simple engines that do\r
-not ponder and do not poll for input while thinking, but it is needed in all\r
-engines. \r
-</p>\r
-</dd>\r
-\r
-<dt>draw</dt>\r
-<dd>The engine's opponent offers the engine a draw. To accept the\r
-draw, send "offer draw". To decline, ignore the offer (that is, send\r
-nothing). If you're playing on ICS, it's possible for the draw offer\r
-to have been withdrawn by the time you accept it, so don't assume the\r
-game is over because you accept a draw offer. Continue playing until\r
-xboard tells you the game is over. See also "offer draw" below.\r
-</dd>\r
-\r
-<dt>result RESULT {COMMENT}</dt>\r
-<dd>After the end of each game, xboard will send you a result command.\r
-You can use this command to trigger learning. RESULT is either 1-0,\r
-0-1, 1/2-1/2, or *, indicating whether white won, black won, the game\r
-was a draw, or the game was unfinished. The COMMENT string is purely\r
-a human-readable comment; its content is unspecified and subject to\r
-change. In ICS mode, it is passed through from ICS uninterpreted.\r
-Example: <pre>result 1-0 {White mates}</pre>\r
-<p>\r
-Here are some notes on interpreting the "result" command. Some apply\r
-only to playing on ICS ("Zippy" mode).\r
-</p>\r
-\r
-<p>\r
-If you won but did not just play a mate, your opponent must have\r
-resigned or forfeited. If you lost but were not just mated, you\r
-probably forfeited on time, or perhaps the operator resigned manually.\r
-If there was a draw for some nonobvious reason, perhaps your opponent\r
-called your flag when he had insufficient mating material (or vice\r
-versa), or perhaps the operator agreed to a draw manually.\r
-</p>\r
-\r
-<p>\r
-You will get a result command even if you already know the game ended\r
--- for example, after you just checkmated your opponent. In fact, if\r
-you send the "RESULT {COMMENT}" command (discussed below), you will\r
-simply get the same thing fed back to you with "result" tacked in\r
-front. You might not always get a "result *" command, however. In\r
-particular, you won't get one in local chess engine mode when the user\r
-stops playing by selecting Reset, Edit Game, Exit or the like.\r
-</p>\r
-</dd>\r
-\r
-<dt><span class="version1">setboard FEN</span></dt>\r
-<dd>\r
-<p><span class="version1">\r
-The setboard command is the new way to set up positions, beginning\r
-in protocol version 2. It is not used unless it has been selected\r
-with the feature command. Here FEN is a position in Forsythe-Edwards\r
-Notation, as defined in the PGN standard.</span>\r
-<span class="version43">Note that this PGN standard referred to here\r
-only applies to normal Chess;\r
-Obviously in variants that cannot be described by a FEN for normal Chess,\r
-e.g. because the board is not 8x8, other pieces then PNBRQK participate, \r
-there are holdings that need to be specified, etc., \r
-xboard will use a FEN format that is standard or suitable for that varant.\r
-In particular, in FRC or CRC, WinBoard will use Shredder-FEN or X-FEN standard,\r
-i.e. it can use the rook-file indicator letter to represent a castling right \r
-(like HAha) whenever it wants, but if it uses KQkq, this will always refer \r
-to the outermost rook on the given side.</span>\r
-</p>\r
-\r
-<p class="version1">\r
-<em>Illegal positions:</em> Note that either setboard or edit can\r
-be used to send an illegal position to the engine. The user can\r
-create any position with xboard's Edit Position command (even, say,\r
-an empty board, or a board with 64 white kings and no black ones).\r
-If your engine receives a position that it considers illegal, \r
-I suggest that you send the response "tellusererror Illegal position",\r
-and then respond to any attempted move with "Illegal move" until\r
-the next new, edit, or setboard command.\r
-</p>\r
-</dd>\r
-\r
-<dt>edit</dt>\r
-<dd>\r
-<p><span class="version1">\r
-The edit command is the old way to set up positions. For compatibility\r
-with old engines, it is still used by default, but new engines may prefer\r
-to use the feature command (see below) to cause xboard to use setboard instead.\r
-</span>\r
-The edit command puts the chess engine into a special mode, where\r
-it accepts the following subcommands:</p>\r
-<table>\r
-<tr><td>c</td><td>change current piece color, initially white</td></tr>\r
-<tr><td>Pa4 (for example)</td><td>place pawn of current color on a4</td></tr>\r
-<tr><td>xa4 (for example)</td><td>empty the square a4 (not used by xboard)</td></tr>\r
-<tr><td>#</td><td>clear board</td></tr>\r
-<tr><td>.</td><td>leave edit mode</td></tr>\r
-</table>\r
-<p class="version1">\r
-See the Idioms section below for additional subcommands used in\r
-ChessBase's implementation of the protocol.\r
-</p>\r
-\r
-<p>The edit command does not change the side to move. To set up a\r
-black-on-move position, xboard uses the following command sequence:\r
-</p>\r
-<pre>\r
- new\r
- force\r
- a2a3\r
- edit\r
- <edit commands>\r
- .\r
-</pre>\r
-\r
-<p>\r
-This sequence is used to avoid the "black" command, which is now\r
-considered obsolete and which many engines never did implement as \r
-specified in this document.\r
-</p>\r
-\r
-<p>\r
-After an edit command is complete, if a king and a rook are on their\r
-home squares, castling is assumed to be available to them. En passant\r
-capture is assumed to be illegal on the current move regardless of the\r
-positions of the pawns. The clock for the 50 move rule starts at\r
-zero, and for purposes of the draw by repetition rule, no prior\r
-positions are deemed to have occurred.\r
-<span class="version43">\r
-In FRC or CRC, any rook and king put on the back rank should be considered to\r
-have castling rights, even if it later becomes apparent that they cannot be both in the\r
-initial position, because the position just set up is asymmetric.\r
-It is upto WinBoard to find work-around in cases where this is not desired,\r
-similar to the "black kludge" shown above, by setting up an earlier position,\r
-and then do a move to destroy castling rights or create e.p. rights.\r
-(Don't bet your life on it...)\r
-</span>\r
-</p>\r
-</dd>\r
-\r
-<dt>hint</dt>\r
-<dd>If the user asks for a hint, xboard sends your engine the command\r
-"hint". Your engine should respond with "Hint: xxx", where xxx is a\r
-suggested move. If there is no move to suggest, you can ignore the\r
-hint command (that is, treat it as a no-op).\r
-</dd>\r
-\r
-<dt>bk</dt>\r
-<dd>If the user selects "Book" from the xboard menu, xboard will send\r
-your engine the command "bk". You can send any text you like as the\r
-response, as long as each line begins with a blank space or tab (\t)\r
-character, and you send an empty line at the end. The text pops up in\r
-a modal information dialog.\r
-</dd>\r
-\r
-<dt>undo</dt>\r
-<dd>If the user asks to back up one move, xboard will send you the\r
-"undo" command. xboard will not send this command without putting you\r
-in "force" mode first, so you don't have to worry about what should\r
-happen if the user asks to undo a move your engine made. (GNU Chess 4\r
-actually switches to playing the opposite color in this case.)\r
-</dd>\r
-\r
-<dt>remove</dt>\r
-<dd>If the user asks to retract a move, xboard will send you the\r
-"remove" command. It sends this command only when the user is on\r
-move. Your engine should undo the last two moves (one for each\r
-player) and continue playing the same color.\r
-</dd>\r
-\r
-<dt>hard</dt>\r
-<dd>Turn on pondering (thinking on the opponent's time, also known as\r
-"permanent brain"). xboard will not make any assumption about what\r
-your default is for pondering or whether "new" affects this setting.\r
-</dd>\r
-\r
-<dt>easy</dt>\r
-<dd>Turn off pondering.</dd>\r
- \r
-<dt>post</dt>\r
-<dd>Turn on thinking/pondering output. \r
-See <a href="#10">Thinking Output</a> section.</dd>\r
-\r
-<dt>nopost</dt>\r
-<dd>Turn off thinking/pondering output.</dd>\r
- \r
-<dt>analyze</dt>\r
-<dd>Enter analyze mode. See <a href="#12">Analyze Mode</a> section.</dd>\r
-\r
-<dt>name X </dt>\r
-<dd>This command informs the engine of its\r
-opponent's name. When the engine is playing on a chess server, xboard\r
-obtains the opponent's name from the server. \r
-<span class="version1">\r
-When the engine is\r
-playing locally against a human user, xboard obtains the user's login\r
-name from the local operating system. When the engine is playing\r
-locally against another engine, xboard uses either the other engine's\r
-filename or the name that the other engine supplied in the myname\r
-option to the feature command. By default, xboard uses the name\r
-command only when the engine is playing on a chess server. Beginning\r
-in protocol version 2, you can change this with the name option to the\r
-feature command; see below.\r
-</span>\r
-</dd>\r
-\r
-<dt>rating</dt>\r
-<dd>In ICS mode, xboard obtains the ICS opponent's rating from the\r
-"Creating:" message that appears before each game. (This message may\r
-not appear on servers using outdated versions of the FICS code.) In\r
-Zippy mode, it sends these ratings on to the chess engine using the\r
-"rating" command. The chess engine's own rating comes first, and if\r
-either opponent is not rated, his rating is given as 0. \r
-<span class="version1">\r
-In the future this command may also be used in other modes, if ratings\r
-are known.\r
-</span>\r
-Example: <pre>rating 2600 1500</pre>\r
-</dd>\r
-\r
-<dt><span class="version1">ics HOSTNAME</span></dt>\r
-<dd class="version1">\r
-If HOSTNAME is "-", the engine is playing against a local\r
-opponent; otherwise, the engine is playing on an Internet Chess Server\r
-(ICS) with the given hostname. This command is new in protocol\r
-version 2 and is not sent unless the engine has enabled it with\r
-the "feature" command. Example: "ics freechess.org"\r
-</dd>\r
-\r
-<dt>computer</dt>\r
-<dd>The opponent is also a computer chess engine. Some engines alter\r
-their playing style when they receive this command.\r
-</dd>\r
-\r
-<dt class="version1">pause</dt>\r
-<dt class="version1">resume</dt>\r
-<dd class="version1">(These commands are new in protocol\r
-version 2 and will not be sent unless feature pause=1 is set. At\r
-this writing, xboard actually does not use the commands at all, but it\r
-or other interfaces may use them in the future.)\r
-The "pause" command puts the engine into a special state where it\r
-does not think, ponder, or otherwise consume significant CPU time.\r
-The current thinking or pondering (if any) is suspended and both\r
-player's clocks are stopped. The only command that the interface may\r
-send to the engine while it is in the paused state is "resume". The\r
-paused thinking or pondering (if any) resumes from exactly where it\r
-left off, and the clock of the player on move resumes running from\r
-where it stopped.\r
-</dd>\r
-\r
-<dt class="version44">memory N</dt>\r
-<dd class="version44">\r
-This command informs the engine on how much memory it is allowed to use maximally, in MegaBytes.\r
-On receipt of this command, the engine should adapt the size of its hash tables accordingly.\r
-This command does only fix the total memory use,\r
-the engine has to decide for itself \r
-(or be configured by the user by other means) \r
-how to divide up the available memory between the various tables it wants to use \r
-(e.g. main hash, pawn hash, tablebase cache, bitbases).\r
-This command will only be sent to engines that have requested it through the memory feature,\r
-and only at the start of a game,\r
-as the first of the commands to relay engine option settings just before each "new" command.\r
-</dd>\r
-\r
-<dt class="version44">cores N</dt>\r
-<dd class="version44">\r
-This command informs the engine on how many CPU cores it is allowed to use maximally.\r
-This could be interpreted as the number of search threads for SMP engines. \r
-(Threads that do not consume significant amounts of CPU time, like I/O threads, need not be included in the count.)\r
-This command will only be sent to engines that have requested it through the smp feature.\r
-The engine should be able to respond to the "cores" command any time during a game,\r
-but it is allowed to finish a search in progress before procesing the command.\r
-(Obeying the command should take priority over finishing a ponder search, though.)\r
-In any case it will be sent at the start of every game\r
-as the last command to relay engine option settings before the "new" command.\r
-</dd>\r
-\r
-<dt class="version44">egtpath TYPE PATH</dt>\r
-<dd class="version44">\r
-This command informs the engine in which directory (given by the PATH argument)\r
-it can find end-game tables of the specified TYPE.\r
-The TYPE argument can be any character string which does not contain spaces.\r
-Currently <strong>nalimov</strong> and <strong>scorpio</strong> are defined types, \r
-for Nalimov tablebases and Scorpio bitbases, respectively,\r
-but future developers of other formats are free to define their own format names.\r
-The GUI simply matches the TYPE names the engine says it supports \r
-with those that the user supplied when configuring xboard.\r
-For every match, it sends a separate "y" command.\r
-The PATH argument would normally (for Nalimov) be the pathname of the directory the EGT files are in,\r
-but could also be the name of a file, or in fact anything the particular EGT type requires.\r
-It is upto the developer of the EGT format to specify the syntax of this parameter.\r
-This command will only be sent to engines that have told the GUI they support EGTs of the given TYPE\r
-through the egt feature.\r
-It will be sent at the start of each game, before the "new" command.\r
-</dd>\r
-\r
-<dt class="version44">option NAME[=VALUE]</dt>\r
-<dd class="version44">\r
-This command changes the setting of the option NAME defined by the engine \r
-(through an earlier feature command)\r
-to the given VALUE.\r
-XBoard will in general have no idea what the option means,\r
-and will send the command only when a user changes the value of this option through a menu,\r
-or at startup of the engine \r
-(before the first 'cores' command or, if that is not sent, the first 'new' command)\r
-in reaction to command-line options.\r
-The NAME echoes back to the engine the string that was identified as an option NAME\r
-in the feature command defining the option.\r
-The VALUE is of the type (numeric or text or absent) that was implied by the option type\r
-specified in this feature command,\r
-i.e. with 'spin' and 'check' options VALUE will be a decimal integer (in the latter case 0 or 1),\r
-with 'combo' and 'string' options VALUE will be a text string,\r
-and with 'button' and 'save' options no VALUE will be sent at all.\r
-</dd>\r
-</dl>\r
-\r
-<h3>Bughouse commands:</h3>\r
-\r
-<p>\r
-xboard now supports bughouse engines when in Zippy mode. See\r
-<a href="http://www.tim-mann.org/xboard/zippy.README"\r
->zippy.README</a> for information on Zippy mode and how to turn on the\r
-bughouse support. The bughouse move format is given above. xboard\r
-sends the following additional commands to the engine when in bughouse\r
-mode. \r
-Commands to inform your engine of the partner's game state may\r
-be added in the future.\r
-</p>\r
-\r
-<dl>\r
-<dt>partner <player></dt>\r
-<dd><player> is now your partner for future games. Example: <pre>partner mann</pre>\r
-</dd>\r
-\r
-<dt>partner</dt>\r
-<dd>Meaning: You no longer have a partner.\r
-</dd>\r
-\r
-<dt>ptell <text></dt>\r
-<dd>Your partner told you <text>, either with a ptell or an ordinary tell. \r
-</dd>\r
-\r
-<dt>holding [<white>] [<black>]</dt>\r
-<dd>White currently holds <white>; black currently holds <black>.\r
- Example: <pre>holding [PPPRQ] []</pre></dd>\r
-\r
-<dt>holding [<white>] [<black>] <color><piece></dt>\r
-<dd>White currently holds <white>; black currently holds <black>, after\r
- <color> acquired <piece>. Example: <pre>holding [PPPRQ] [R] BR</pre></dd>\r
-</dl>\r
-\r
-<h2><a name="9">9. Commands from the engine to xboard</a></h2>\r
-\r
-<p class="version1">\r
-In general, an engine should not send any output to xboard that is not\r
-described in this document. As the protocol is extended, newer\r
-versions of xboard may recognize additional strings as commands that\r
-were previously not assigned a meaning.\r
-</p>\r
-\r
-<dl>\r
-\r
-<dt class="version1"> feature FEATURE1=VALUE1 FEATURE2=VALUE2 ... </dt>\r
-<dd class="version1">\r
-<p>Beginning with version 2, the protocol includes the "feature"\r
-command, which lets your engine control certain optional protocol\r
-features. Feature settings are written as FEATURE=VALUE, where\r
-FEATURE is a name from the list below and VALUE is the value to be\r
-assigned. Features can take string, integer, or boolean values; the\r
-type of value is listed for each feature. String values are written\r
-in double quotes (for example, <tt>feature myname="Miracle Chess\r
-0.9"</tt>), integers are written in decimal, and boolean values are\r
-written as 0 for false, 1 for true. Any number of features can be set\r
-in one feature command, or multiple feature commands can be given.</p>\r
-\r
-<p>\r
-Your engine should send one or more feature commands immediately after\r
-receiving the "protover" command, since xboard needs to know the\r
-values of some features before sending further commands to the engine.\r
-Because engines that predate protocol version 2 do not send "feature",\r
-xboard uses a timeout mechanism: when it first starts your engine, it\r
-sends "xboard" and "protover N", then listens for feature commands for\r
-two seconds before sending any other commands. To end this timeout\r
-and avoid the wait, set the feature "done=1" at the end of your last\r
-feature command. To increase the timeout, if needed, set the feature\r
-"done=0" before your first feature command and "done=1" at the end.\r
-If needed, it is okay for your engine to set done=0 soon as it starts,\r
-even before it receives the xboard and protover commands. This can be\r
-useful if your engine takes a long time to initialize itself. It\r
-should be harmless even if you are talking to a (version 1) user\r
-interface that does not understand the "feature" command, since such\r
-interfaces generally ignore commands from the engine that they do not\r
-understand.\r
-</p>\r
-\r
-<p>\r
-The feature command is designed to let the protocol change without\r
-breaking engines that were written for older protocol versions. When\r
-a new feature is added to the protocol, its default value is always\r
-chosen to be compatible with older versions of the protocol that did\r
-not have the feature. Any feature that your engine does not set in a\r
-"feature" command retains its default value, so as the protocol\r
-changes, you do not have to change your engine to keep up with it\r
-unless you want to take advantage of a new feature. Because some\r
-features are improvements to the protocol, while others are meant to\r
-cater to engines that do not implement all the protocol features, the\r
-recommended setting for a feature is not always the same as the\r
-default setting. The listing below gives both default and recommended\r
-settings for most features.\r
-</p>\r
-\r
-<p>\r
-You may want to code your engine so as to be able to work with\r
-multiple versions of the engine protocol. Protocol version 1 does not\r
-send the protover command and does not implement the feature command;\r
-if you send a feature command in protocol version 1, it will have no\r
-effect and there will be no response. In protocol version 2 or later,\r
-each feature F that you set generates the response "accepted F" if the\r
-feature is implemented, or "rejected F" if it is not. Thus an engine\r
-author can request any feature without having to keep track of which\r
-protocol version it was introduced in; you need only check whether the\r
-feature is accepted or rejected. This mechanism also makes it\r
-possible for a user interface author to implement a subset of a\r
-protocol version by rejecting some features that are defined in that\r
-version; however, you should realize that engine authors are likely to\r
-code for xboard and may not be prepared to have a feature that they\r
-depend on be rejected.\r
-<span class="version44">If the GUI rejects an option feature because of the\r
-syntax of the value, it should print the value string with the\r
-"rejected" command, e.g. "rejected option nonsense" in response\r
-to receiving feature option="nonsense".</span>\r
-</p>\r
-\r
-<p>\r
-Here are the features that are currently defined.\r
-</p>\r
-\r
-<dl>\r
-<dt class="version1">ping (boolean, default 0, recommended 1)</dt>\r
-<dd class="version1">\r
-If ping=1, xboard may use the protocol's new "ping" command;\r
-if ping=0, xboard will not use the command.\r
-</dd>\r
-\r
-<dt class="version1">setboard (boolean, default 0, recommended 1)</dt>\r
-<dd class="version1">\r
-If setboard=1, xboard will use the protocol's new "setboard" command\r
-to set up positions; if setboard=0, it will use the older "edit" command.\r
-</dd>\r
-\r
-<dt class="version1">playother (boolean, default 0, recommended 1)</dt>\r
-<dd class="version1">\r
-If playother=1, xboard will use the protocol's new "playother" command\r
-when appropriate; if playother=0, it will not use the command.\r
-</dd>\r
-\r
-<dt class="version1">san (boolean, default 0)</dt>\r
-<dd class="version1">\r
-If san=1, xboard will send moves to the engine in standard algebraic\r
-notation (SAN); for example, Nf3. If san=0, xboard will send moves in\r
-coordinate notation; for example, g1f3. See MOVE in \r
-<a href="#8">section 8</a> above for more details of both kinds of notation.\r
-</dd>\r
-\r
-<dt class="version1">usermove (boolean, default 0)</dt>\r
-<dd class="version1">\r
-If usermove=1, xboard will send moves to the engine with the\r
-command "usermove MOVE"; if usermove=0, xboard will send just the move,\r
-with no command name.\r
-</dd>\r
-\r
-<dt class="version1">time (boolean, default 1, recommended 1)</dt>\r
-<dd class="version1">\r
-If time=1, xboard will send the "time" and "otim" commands to\r
-update the engine's clocks; if time=0, it will not.\r
-</dd>\r
-\r
-<dt class="version1">draw (boolean, default 1, recommended 1)</dt>\r
-<dd class="version1">\r
-If draw=1, xboard will send the "draw" command if the engine's opponent\r
-offers a draw; if draw=0, xboard will not inform the engine about\r
-draw offers. Note that if draw=1, you may receive a draw offer while you\r
-are on move; if this will cause you to move immediately, you should set\r
-draw=0.\r
-</dd>\r
-\r
-<dt class="version1">sigint (boolean, default 1)</dt>\r
-<dd class="version1">\r
-If sigint=1, xboard may send SIGINT (the interrupt signal) to\r
-the engine as <a href="#7">section 7</a> above; if sigint=0, it will\r
-not.\r
-</dd>\r
-\r
-<dt class="version1">sigterm (boolean, default 1)</dt>\r
-<dd class="version1">\r
-If sigterm=1, xboard may send SIGTERM (the termination signal) to\r
-the engine as <a href="#7">section 7</a> above; if sigterm=0, it will\r
-not.\r
-</dd>\r
-\r
-<dt class="version1">reuse (boolean, default 1, recommended 1) </dt>\r
-<dd class="version1">\r
-If reuse=1, xboard may reuse your engine for multiple games. If\r
-reuse=0 (or if the user has set the -xreuse option on xboard's command\r
-line), xboard will kill the engine process after every game and start\r
-a fresh process for the next game.\r
-</dd>\r
-\r
-<dt class="version1">analyze (boolean, default 1, recommended 1)</dt>\r
-<dd class="version1">\r
-If analyze=0, xboard will not try to use the "analyze" command; it\r
-will pop up an error message if the user asks for analysis mode. If\r
-analyze=1, xboard will try to use the command if the user asks for\r
-analysis mode.\r
-</dd>\r
-\r
-<dt class="version1">myname (string, default determined from engine filename)</dt>\r
-<dd class="version1">\r
-This feature lets you set the name that xboard will use for your\r
-engine in window banners, in the PGN tags of saved game files, and when\r
-sending the "name" command to another engine.\r
-</dd>\r
-\r
-<dt class="version1">variants (string, see text below)</dt>\r
-<dd><span class="version1">\r
-This feature indicates which chess variants your engine accepts.\r
-It should be a comma-separated list of variant names. See the table\r
-under the "variant" command in <a href="#8">section 8</a> above. If\r
-you do not set this feature, xboard will assume by default that your\r
-engine supports all variants. (However, the -zippyVariants\r
-command-line option still limits which variants will be accepted in\r
-Zippy mode.) It is recommended that you set this feature to the\r
-correct value for your engine (just "normal" in most cases) rather\r
-than leaving the default in place, so that the user will get an\r
-appropriate error message if he tries to play a variant that your\r
-engine does not support.</span>\r
-<br />\r
-<span class="version43">If your engine can play variants on a deviating board size,\r
-like capablanca on an 8x8 board, or capablanca crazyhouse,\r
-it can list them amongst the variants with a prefix spcifying board size plus\r
-holdings size, like 8x8+0_capablanca or 10x8+7_capablanca.\r
-If it is capable of playing any variant with an arbitrary board size,\r
-it should list "boardsize" as one of the variants.\r
-If there is a maximum to the board size, this can be prefixed,\r
-e.g. "12x10+0_boardsize".\r
-</span>\r
-</dd>\r
-\r
-<dt class="version1">colors (boolean, default 1, recommended 0) </dt>\r
-<dd><span class="version1">\r
-If colors=1, xboard uses the obsolete "white" and "black"\r
-commands in a stylized way that works with most older chess engines\r
-that require the commands. See the "<a href="#13">Idioms</a>" section\r
-below for details. If colors=0, xboard does not use the "white" and\r
-"black" commands at all.\r
-</span>\r
-</dd>\r
-\r
-<dt class="version1">ics (boolean, default 0)</dt>\r
-<dd class="version1">\r
-If ics=1, xboard will use the protocol's new "ics" command\r
-to inform the engine of whether or not it is playing on a chess server;\r
-if ics=0, it will not.\r
-</dd>\r
-\r
-<dt class="version1">name (boolean, see text below)</dt>\r
-<dd class="version1">\r
-If name=1, xboard will use the protocol's "name" command\r
-to inform the engine of the opponent's name; if name=0, it will not.\r
-By default, name=1 if the engine is playing on a chess server; name=0 if not.\r
-</dd>\r
-\r
-<dt class="version1">pause (boolean, default 0)</dt>\r
-<dd class="version1">\r
-If pause=1, xboard may use the protocol's new "pause" command;\r
-if pause=0, xboard assumes that the engine does not support this command.\r
-</dd>\r
-\r
-<dt class="version43">nps (boolean, default ?)</dt>\r
-<dd class="version43">\r
-If nps=1, it means the engine supports the nps command.\r
-If nps=0, it means the engine does not support it, and WinBoard should refrain from sending it.\r
-Default is that WinBoard sends it, in an attempt to try out if the engine understand it.\r
-The engine should properly respond with "Error (unkown command): nps" if it does not implement it,\r
-(as any protocol version pre-scribes),\r
-or WinBoard might assume that the engine did understand the command. \r
-In that case the use of different time standards that ensues could lead to time forfeits for the engine.\r
-</dd>\r
-\r
-<dt class="version43">debug (boolean, default 0)</dt>\r
-<dd class="version43">\r
-If debug=1, it means the engine wants to send debug output prefixed by '#',\r
-which WinBoard should ignore, except for including it in the winboard.debug file.\r
-As this feature is added to protocol 2 ony late,\r
-so that not all protocol-2 supporting versions of WinBoard might implement it,\r
-it is important that engines check if WinBoard accepts the feature.\r
-If the feature is rejected,\r
-engines must refrain from sending the debug output,\r
-or do so at their own risk.\r
-</dd>\r
-\r
-<dt class="version44">memory (boolean, default 0)</dt>\r
-<dd class="version44">\r
-If memory=1, the size of the total amount of memory available for the memory-consuming tables of the engine \r
-(e.g. hash, EGTB cache)\r
-will be set by the GUI through the "memory" command.\r
-</dd>\r
-\r
-<dt class="version44">smp (boolean, default 0)</dt>\r
-<dd class="version44">\r
-If smp=1, the GUI will send the "cores" command to the engine to inform it how many CPU cores it can use.\r
-Note that sending smp=1 does not imply the engine can use more than one CPU;\r
-just that it wants to receive the "cores" command.\r
-</dd>\r
-\r
-<dt class="version44">egt (string, see text below)</dt>\r
-<dd class="version44">\r
-This feature indicates which end-game table formats the engine supports.\r
-It should be a comma-separated list of format names.\r
-See under the "egtpath" command in <a href="#8">section 8</a> above.\r
-If you do not set this feature, xboard will assume the engine does not support end-game tables,\r
-and will not send any "egtpath" commands to inform the engine about their whereabouts.\r
-</dd>\r
-\r
-<dt class="version44">option (string, see text below)</dt>\r
-<dd><span class="version44">\r
-This feature is used by the engine to define an option command to appear in a GUI menu,\r
-so that the user can change the corresponding setting of the engine through the GUI interactively.\r
-The string describes the option by defining a name, type, current value and (sometimes) the acceptable value range.\r
-Unlike other features, option features are accumulated by the GUI, \r
-and the GUI must be able to add a new option to the list at any time,\r
-even after having received feature done=1.\r
-There are ten different options types, each requiring a slighly different syntax of the defining string:\r
-<br />\r
-feature option="NAME -button"\r
-<br />\r
-feature option="NAME -save"\r
-<br />\r
-feature option="NAME -reset"\r
-<br />\r
-feature option="NAME -check VALUE"\r
-<br />\r
-feature option="NAME -string VALUE"\r
-<br />\r
-feature option="NAME -spin VALUE MIN MAX"\r
-<br />\r
-feature option="NAME -combo CHOICE1 /// CHOICE2 ..."\r
-<br />\r
-feature option="NAME -slider VALUE MIN MAX"\r
-<br />\r
-feature option="NAME -file VALUE"\r
-<br />\r
-feature option="NAME -path VALUE"\r
-<br />\r
-NAME is an arbitrary alphanumeric string which can contain spaces; \r
-the other words in capitals would be replaced by the current (default) setting of the option,\r
-(a character string for -string options, a decimal number for -spin and -check options,\r
-were the latter uses 1=checked, 0=unchecked),\r
-the minimum or maximum value of numeric (-spin) options, \r
-or arbitrary text labels (for -combo option).\r
-In the latter case, the current value will be preceded by an asterisk.\r
-The -file and -path options are similar to -string, but can be used to inform the GUI that\r
-the text represents a file name or folder name respectively, \r
-so the GUI dialog could add the appropriate browse button to the text-edit field.\r
-Similarly, a -slider option is like a -spin, but the GUI might make a different\r
-graphical representation for it.\r
-A -save option is like a -button, and defines an immediate command to be sent by the engine.\r
-With -save the GUI will make sure all current option settings are flushed to the engine\r
-before it sends this command.\r
-A -reset option is like a -button, but use of it purges the list of options before sending \r
-the corresponding option command to the engine.\r
-This enables the engine to completely redefine its options or their current settings,\r
-by sending a new set of option feature commands to the GUI, \r
-terminated by feature done=1.\r
-(The effect of sending an option feature for an option with the same name as was defined before, \r
-without first receiving a -reset option command, is undefined.)\r
-</span>\r
-</dd>\r
-\r
-<dt class="version1">done (integer, no default)</dt>\r
-<dd><span class="version1">\r
-If you set done=1 during the initial two-second timeout after\r
-xboard sends you the "xboard" command, the\r
-timeout will end and xboard will not look for any more feature\r
-commands before starting normal operation.\r
-If you set done=0, the initial timeout is increased to one hour;\r
-in this case, you must set done=1 before xboard will enter normal operation.\r
-</span>\r
-</dd>\r
-</dl>\r
-</dd>\r
-\r
-\r
-<dt>Illegal move: MOVE</dt>\r
-<dt>Illegal move (REASON): MOVE</dt>\r
-<dd>If your engine receives a MOVE command that is recognizably a move\r
-but is not legal in the current position, your engine must print an\r
-error message in one of the above formats so that xboard can pass the\r
-error on to the user and retract the move. The (REASON) is entirely\r
-optional. Examples:\r
-\r
-<pre>\r
- Illegal move: e2e4\r
- Illegal move (in check): Nf3\r
- Illegal move (moving into check): e1g1\r
-</pre>\r
-<p>\r
-Generally, xboard will never send an ambiguous move, so it does not \r
-matter whether you respond to such a move with an Illegal move message \r
-or an Error message.\r
-</p>\r
-</dd>\r
-\r
-<dt>Error (ERRORTYPE): COMMAND</dt>\r
-<dd>If your engine receives a command it does not understand or does\r
-not implement, it should print an error message in the above format so\r
-that xboard can parse it. Examples:\r
-<pre>\r
- Error (ambiguous move): Nf3\r
- Error (unknown command): analyze\r
- Error (command not legal now): undo\r
- Error (too many parameters): level 1 2 3 4 5 6 7\r
-</pre>\r
-</dd>\r
-\r
-<dt>move MOVE</dt>\r
-<dd>Your engine is making the move MOVE. Do not echo moves from\r
-xboard with this command; send only new moves made by the engine.\r
-\r
-<div class="version1">\r
-<p>For the actual move text from your chess engine (in place of MOVE\r
-above), your move should be either</p>\r
-<ul>\r
-<li>in coordinate notation (e.g.,\r
-e2e4, e7e8q) with castling indicated by the King's two-square move (e.g.,\r
-e1g1), or</li>\r
-<li>in Standard Algebraic Notation (SAN) as defined in the\r
-Portable Game Notation standard (e.g, e4, Nf3, O-O, cxb5, Nxe4, e8=Q),\r
-with the extension piece@square (e.g., P@f7) to handle piece placement\r
-in bughouse and crazyhouse.</li>\r
-</ul>\r
-<p>\r
-xboard itself also accepts some variants of SAN, but for compatibility\r
-with non-xboard interfaces, it is best not to rely on this behavior.\r
-</p>\r
-\r
-<p>Warning: Even though all versions of this protocol specification\r
-have indicated that xboard accepts SAN moves, some non-xboard\r
-interfaces are known to accept only coordinate notation. See the\r
-Idioms section for more information on the known limitations of some\r
-non-xboard interfaces. It should be safe to send SAN moves if you\r
-receive a "protover 2" (or later) command from the interface, but\r
-otherwise it is best to stick to coordinate notation for maximum\r
-compatibility. An even more conservative approach would be for your\r
-engine to send SAN to the interface only if you have set feature san=1\r
-(which causes the interface to send SAN to you) and have received\r
-"accepted san" in reply.\r
-</p>\r
-</div>\r
-</dd>\r
-\r
-<dt>RESULT {COMMENT}</dt>\r
-<dd>When your engine detects\r
-that the game has ended by rule, your engine must output a line of the\r
-form "RESULT {comment}" (without the quotes), where RESULT is a PGN\r
-result code (1-0, 0-1, or 1/2-1/2), and comment is the reason. Here\r
-"by rule" means that the game is definitely over because of what\r
-happened on the board. In normal chess, this includes checkmate,\r
-stalemate, triple repetition, the 50 move rule, or insufficient\r
-material; it does not include loss on time or the like.\r
-Examples:\r
-<pre>\r
- 0-1 {Black mates}\r
- 1-0 {White mates}\r
- 1/2-1/2 {Draw by repetition}\r
- 1/2-1/2 {Stalemate}\r
-</pre>\r
-\r
-<p>\r
-xboard relays the result to the user, the ICS, the other engine in Two\r
-Machines mode, and the PGN save file as required.\r
-<span class="version43">Note that "definitey over" above means that sending this command \r
-will be taken by WinBoard as an unconditional refusal of the engine to play on,\r
-which might cause you to forfeit if the game was in fact not over.\r
-This command should thus not be used to offer draws, accept draws,\r
-or make draw-by-rule claims that are not yet valid in the current position\r
-(but will be after you move).\r
-For offering and claiming such draws, "offer draw" should be used.</span>\r
-</p>\r
-\r
-<p class="version44">\r
-Note that (in accordance with FIDE rules) only KK, KNK, KBK and KBKB with all bishops on the\r
-same color can be claimed as draws on the basis of insufficient mating material.\r
-The end-games KNNK, KBKN, KNKN and KBKB with unlike bishops do have mate positions,\r
-and cannot be claimed.\r
-Complex draws based on locked Pawn chains will not be recognized as draws by most interfaces,\r
-so do not claim in such positions, but just offer a draw or play on.\r
-</p>\r
-\r
-<p class="version44">\r
-Note to GUI programmers: RESULT commands that the engine sends immediately after its move\r
-might be detected by the GUI only after the opponent has moved, because of communication\r
-and scheduling delays, no matter how fast the engine sent it.\r
-Any judgement of the validity of RESULT claims based on te "current" board position\r
-will have to account for this uncertainty.\r
-</p>\r
-</dd>\r
-\r
-<dt>resign</dt>\r
-<dd>If your engine wants to resign, it can send the command "resign".\r
-Alternatively, it can use the "RESULT {comment}" command if the string\r
-"resign" is included in the comment; for example "0-1 {White\r
-resigns}". xboard relays the resignation to the user, the ICS, the\r
-other engine in Two Machines mode, and the PGN save file as required.\r
-<span class="version44">Note that many interfaces work more smoothly if you resign <em>before</em>\r
-you move.</span>\r
-</dd>\r
-\r
-<dt>offer draw</dt>\r
-<dd>If your engine wants to offer a draw by agreement (as opposed to\r
-claiming a draw by rule), it can send the command "offer draw".\r
-xboard relays the offer to the user, the ICS, the other engine in Two\r
-Machines mode, and the PGN save file as required. In Machine White,\r
-Machine Black, or Two Machines mode, the offer is considered valid\r
-until your engine has made two more moves.\r
-<span class="version43">This command must also be used to accept a draw offer.\r
-Do not use the 1/2-1/2 command for that, as the offer might be no longer valid,\r
-in which case a refusal to play on implied by the RESULT command might make you forfeit the game.\r
-"offer draw" should also be used to claim 50-move and 3-fold-repetition draws\r
-that will occur <em>after</em> your move, by sending it <em>before</em> making the move.\r
-WinBoard will grant draw offers without the opponent having any say in\r
-it in situations where draws can be claimed.\r
-Only if the draw cannot be claimed, the offer will be passed to your opponent after you make your next move,\r
-just before WinBoard relays this move to the opponent.\r
-</span>\r
-</dd>\r
-\r
-<dt class="version1">tellopponent MESSAGE</dt>\r
-<dd class="version1">\r
-This command lets the engine give a message to its opponent,\r
-independent of whether the opponent is a user on the local machine or\r
-a remote ICS user (Zippy mode). MESSAGE consists of any characters,\r
-including whitespace, to the end of the line. When the engine is\r
-playing against a user on the local machine, xboard pops up an\r
-information dialog containing the message. When the engine is playing\r
-against an opponent on the ICS (Zippy mode), xboard sends "say\r
-MESSAGE\n" to the ICS.\r
-</dd>\r
-\r
-<dt class="version1">tellothers MESSAGE </dt>\r
-<dd class="version1">This command lets the engine give a message to people watching the\r
-game other than the engine's opponent. MESSAGE consists of any\r
-characters, including whitespace, to the end of the line. When the\r
-engine is playing against a user on the local machine, this command\r
-does nothing. When the engine is playing against an opponent on the\r
-ICS (Zippy mode), xboard sends "whisper MESSAGE\n" to the ICS.\r
-</dd>\r
-\r
-<dt class="version1">tellall MESSAGE</dt>\r
-<dd class="version1">This command lets the engine give a message to its opponent and\r
-other people watching the game, \r
-independent of whether the opponent is a user on the local machine or\r
-a remote ICS user (Zippy mode). MESSAGE consists of any characters,\r
-including whitespace, to the end of the line. When the engine is\r
-playing against a user on the local machine, xboard pops up an\r
-information dialog containing the message. When the engine is playing\r
-against an opponent on the ICS (Zippy mode), xboard sends "kibitz\r
-MESSAGE\n" to the ICS.\r
-</dd>\r
-\r
-<dt>telluser MESSAGE</dt>\r
-<dd>xboard pops up an information dialog containing the message.\r
-MESSAGE consists of any characters, including whitespace, to the end\r
-of the line.\r
-</dd>\r
-\r
-<dt>tellusererror MESSAGE</dt>\r
-<dd>xboard pops up an error dialog containing the message.\r
-MESSAGE consists of any characters, including whitespace, to the end\r
-of the line.\r
-</dd>\r
-\r
-<dt>askuser REPTAG MESSAGE</dt>\r
-<dd>Here REPTAG is a string containing no whitespace, and MESSAGE\r
-consists of any characters, including whitespace, to the end of the\r
-line. xboard pops up a question dialog that says MESSAGE and\r
-has a typein box. If the user types in "bar", xboard sends "REPTAG\r
-bar" to the engine. The user can cancel the dialog and send nothing.\r
-</dd>\r
-\r
-<dt>tellics MESSAGE</dt>\r
-<dd>In Zippy mode, xboard sends "MESSAGE\n" to ICS. MESSAGE consists\r
-of any characters, including whitespace, to the end of the line.\r
-</dd>\r
-\r
-<dt class="version1">tellicsnoalias MESSAGE</dt>\r
-<dd class="version1">\r
-In Zippy mode, xboard sends "xMESSAGE\n" to ICS, where "x" is a\r
-character that prevents the ICS from expanding command aliases, if\r
-xboard knows of such a character. (On chessclub.com and chess.net,\r
-"/" is used; on freechess.org, "$" is used.) MESSAGE consists of any\r
-characters, including whitespace, to the end of the line.\r
-</dd>\r
-\r
-<dt class="version43"># COMMENT</dt>\r
-<dd class="version43">\r
-The engine can send any string of printable characters, terminated by a newline,\r
-for inclusion in the winboard.debug file, provided the line starts with a '#' character.\r
-If the engine has set feature debug=1,\r
-it is guaranteed that WinBoard (and any future version of it) will completely ignore\r
-these lines in any other respect.\r
-</dd>\r
-</dl>\r
-\r
-<h2><a name="10">10. Thinking Output</a></h2>\r
-\r
-<p>\r
-If the user asks your engine to "show thinking", xboard sends your\r
-engine the "post" command. It sends "nopost" to turn thinking off.\r
-In post mode, your engine sends output lines to show the progress of\r
-its thinking. The engine can send as many or few of these lines as it\r
-wants to, whenever it wants to. Typically they would be sent when the\r
-PV (principal variation) changes or the depth changes. The thinking\r
-output should be in the following format:\r
-</p>\r
-\r
-<pre>ply score time nodes pv</pre>\r
-\r
-<p>Where:</p>\r
-<table>\r
-<tr><td>ply</td><td>Integer giving current search depth.</td></tr>\r
-<tr><td>score</td><td>Integer giving current evaluation in centipawns.</td></tr>\r
-<tr><td>time</td><td>Current search time in centiseconds (ex:1028 = 10.28 seconds).</td></tr>\r
-<tr><td>nodes</td><td>Nodes searched.</td></tr>\r
-<tr><td>pv</td><td>Freeform text giving current "best" line.\r
-You can continue the pv onto another line if you start each\r
-continuation line with at least four space characters.</td></tr>\r
-</table>\r
-\r
-<p>\r
-Example:\r
-</p>\r
-\r
-<pre> 9 156 1084 48000 Nf3 Nc6 Nc3 Nf6</pre>\r
-\r
-<p>\r
-Meaning:\r
-</p>\r
-\r
-<pre>\r
-9 ply, score=1.56, time = 10.84 seconds, nodes=48000, PV = "Nf3 Nc6 Nc3 Nf6"\r
-</pre>\r
-\r
-<p>\r
-Longer example from actual Crafty output:\r
-</p>\r
-\r
-<pre>\r
- 4 109 14 1435 1. e4 d5 2. Qf3 dxe4 3. Qxe4 Nc6\r
- 4 116 23 2252 1. Nf3 Nc6 2. e4 e6\r
- 4 116 27 2589 1. Nf3 Nc6 2. e4 e6\r
- 5 141 44 4539 1. Nf3 Nc6 2. O-O e5 3. e4\r
- 5 141 54 5568 1. Nf3 Nc6 2. O-O e5 3. e4\r
-</pre>\r
-\r
-<p>\r
-You can use the PV to show other things; for instance, while in book,\r
-Crafty shows the observed frequency of different reply moves in its\r
-book. In situations like this where your engine is not really\r
-searching, start the PV with a '(' character:\r
-</p>\r
-\r
-<pre>\r
- 0 0 0 0 (e4 64%, d4 24%)\r
-</pre>\r
-\r
-<p>\r
-GNU Chess output is very slightly different. The ply number is\r
-followed by an extra nonblank character, and the time is in seconds,\r
-not hundredths of seconds. For compatibility, xboard accepts the\r
-extra character and takes it as a flag indicating the different time\r
-units. Example:\r
-</p>\r
-\r
-<pre>\r
- 2. 14 0 38 d1d2 e8e7 \r
- 3+ 78 0 65 d1d2 e8e7 d2d3 \r
- 3& 14 0 89 d1d2 e8e7 d2d3 \r
- 3& 76 0 191 d1e2 e8e7 e2e3 \r
- 3. 76 0 215 d1e2 e8e7 e2e3 \r
- 4& 15 0 366 d1e2 e8e7 e2e3 e7e6 \r
- 4. 15 0 515 d1e2 e8e7 e2e3 e7e6 \r
- 5+ 74 0 702 d1e2 f7f5 e2e3 e8e7 e3f4 \r
- 5& 71 0 1085 d1e2 e8e7 e2e3 e7e6 e3f4 \r
- 5. 71 0 1669 d1e2 e8e7 e2e3 e7e6 e3f4 \r
- 6& 48 0 3035 d1e2 e8e7 e2e3 e7e6 e3e4 f7f5 e4d4 \r
- 6. 48 0 3720 d1e2 e8e7 e2e3 e7e6 e3e4 f7f5 e4d4 \r
- 7& 48 0 6381 d1e2 e8e7 e2e3 e7e6 e3e4 f7f5 e4d4 \r
- 7. 48 0 10056 d1e2 e8e7 e2e3 e7e6 e3e4 f7f5 e4d4 \r
- 8& 66 1 20536 d1e2 e8e7 e2e3 e7e6 e3d4 g7g5 a2a4 f7f5 \r
- 8. 66 1 24387 d1e2 e8e7 e2e3 e7e6 e3d4 g7g5 a2a4 f7f5 \r
- 9& 62 2 38886 d1e2 e8e7 e2e3 e7e6 e3d4 h7h5 a2a4 h5h4 \r
- d4e4 \r
- 9. 62 4 72578 d1e2 e8e7 e2e3 e7e6 e3d4 h7h5 a2a4 h5h4 \r
- d4e4 \r
-10& 34 7 135944 d1e2 e8e7 e2e3 e7e6 e3d4 h7h5 c2c4 h5h4 \r
- d4e4 f7f5 e4f4 \r
-10. 34 9 173474 d1e2 e8e7 e2e3 e7e6 e3d4 h7h5 c2c4 h5h4 \r
- d4e4 f7f5 e4f4 \r
-</pre>\r
-\r
-<p>If your engine is pondering (thinking on its opponent's time) in post\r
-mode, it can show its thinking then too. In this case your engine may\r
-omit the hint move (the move it is assuming its opponent will make)\r
-from the thinking lines <em>if and only if</em> it sends xboard the move in\r
-the usual "Hint: xxx" format before sending the first line.\r
-</p>\r
-\r
-<h2><a name="11">11. Time control</a></h2>\r
-\r
-<p>\r
-xboard supports three styles of time control: conventional chess clocks,\r
-the ICS-style incremental clock, and an exact number of seconds per move.\r
-</p>\r
-\r
-<p>In conventional clock mode, every time control period is the same.\r
-That is, if the time control is 40 moves in 5 minutes, then after each\r
-side has made 40 moves, they each get an additional 5 minutes, and so\r
-on, ad infinitum. At some future time it would be nice to support a\r
-series of distinct time controls. This is very low on my personal\r
-priority list, but code donations to the xboard project are accepted,\r
-so feel free to take a swing at it. I suggest you talk to me first,\r
-though.\r
-</p>\r
-\r
-<p>\r
-The command to set a conventional time control looks like this:\r
-</p>\r
-\r
-<pre>\r
- level 40 5 0\r
- level 40 0:30 0\r
-</pre>\r
-\r
-<p>\r
-The 40 means that there are 40 moves per time control. The 5 means\r
-there are 5 minutes in the control. In the second example, the 0:30\r
-means there are 30 seconds. The final 0 means that we are in\r
-conventional clock mode.\r
-</p>\r
-\r
-<p class="version43">\r
-Note that the time parameter in this command is not a pure numeric argument,\r
-but in general is a character string, in order to pass the number of seconds.\r
-Engines are encouraged to ignore any unexpected characters at the end of this string,\r
-i.e. following the MIN or MIN:SEC specification.\r
-Future protocol versions might (under control of an appropriate feature)\r
-append such extra characters to this argument,\r
-in order to inform the engine in advance of the time control it can expect after the current session completes.\r
-E.g. "level 40 25+5 0" could mean that the engine has to play 40 moves in 25 minutes,\r
-but should expect to get only 5 minutes for the entire remainder of the game after that,\r
-rather than another 25 minutes for the next 40 moves.\r
-When the time comes, (i.e. after the 40 moves), \r
-it will be informed of the time-control change by receiving a new "level 0 5 0" command,\r
-but engines with advanced time management might want to plan for this in advance.\r
-</p>\r
-\r
-<p>\r
-The command to set an incremental time control looks like this:\r
-</p>\r
-\r
-<pre>\r
- level 0 2 12\r
-</pre>\r
-\r
-<p>\r
-Here the 0 means "play the whole game in this time control period",\r
-the 2 means "base=2 minutes", and the 12 means "inc=12 seconds". As\r
-in conventional clock mode, the second argument to level can be in\r
-minutes and seconds.\r
-</p>\r
-\r
-<p>\r
-At the start of the game, each player's clock is set to base minutes.\r
-Immediately after a player makes a move, inc seconds are added to his\r
-clock. A player's clock counts down while it is his turn. Your flag\r
-can be called whenever your clock is zero or negative. (Your clock\r
-can go negative and then become positive again because of the\r
-increment.)\r
-</p>\r
-\r
-<p class="version44">\r
-The number of moves given in the level command (when non-zero) should \r
-be taken as the number of moves still to do before the specified time\r
-will be added to the clock, if the "level" command is received after\r
-some moves have already been played.\r
-The time given should be interpreted as the time left on its clock\r
-(including any time left over from the previous sessions),\r
-and not necessarily the time that will be added to the clock\r
-after the specified number of moves has been played.\r
-This is only relevant in WinBoard 4.3.xx, which might send the engine\r
-"level" commands during a game,\r
-just before the engine has to start thinking about the first move of \r
-a new time-control session.\r
-Example: if at the start of the game "level 40 60 0" was given \r
-(40 moves per hour),\r
-and the engine receives "level 20 22 0" just before move 41,\r
-it should understand that it should do the next 20 moves in 22 minutes\r
-(pehaps because the secondary session was 20 moves per 15 minutes,\r
-and it had 7 minutes left on its clock after the first 40 moves).\r
-</p>\r
-\r
-<p>\r
-A special rule on some ICS implementations: if you ask for a game with\r
-base=0, the clocks really start at 10 seconds instead of 0. xboard\r
-itself does not know about this rule, so it passes the 0 on to the\r
-engine instead of changing it to 0:10.\r
-</p>\r
-\r
-<p>\r
-ICS also has time odds games. With time odds, each player has his own\r
-(base, inc) pair, but otherwise things work the same as in normal\r
-games. The Zippy xboard accepts time odds games but ignores the fact\r
-that the opponent's parameters are different; this is perhaps not\r
-quite the right thing to do, but gnuchess doesn't understand time\r
-odds. Time odds games are always unrated.\r
-</p>\r
-\r
-<p>\r
-The command to set an exact number of seconds per move looks like this:\r
-</p>\r
-\r
-<pre>\r
- st 30\r
-</pre>\r
-\r
-<p>\r
-This means that each move must be made in at most 30 seconds. Time not used\r
-on one move does not accumulate for use on later moves.\r
-</p>\r
-\r
-<h2><a name="12">12. Analyze Mode</a></h2>\r
-\r
-<p>xboard supports analyzing fresh games, edited positions, and games\r
-from files. However, all of these look the same from the chess\r
-engine's perspective. Basically, the engine just has to respond to the\r
-"analyze" command. \r
-<span class="version1">\r
-Beginning in protocol version 2,\r
-if your engine does not support analyze mode, it should use\r
-the feature command to set analyze=0. \r
-</span>\r
-The older method of\r
-printing the error message "Error (unknown command): analyze" in\r
-response to the "analyze" command will also work, however.\r
-</p>\r
-\r
-<p>\r
-To enter analyze mode, xboard sends the command sequence "post", "analyze". \r
-Analyze mode in your engine should be\r
-similar to force mode, except that your engine thinks about what move\r
-it would make next if it were on move. Your engine should accept the\r
-following commands while in analyze mode:\r
-</p>\r
-\r
-<ul>\r
-<li>Any legal move, as in force mode</li>\r
-<li><strong>undo</strong> Back up one move and analyze previous position.</li>\r
-<li><strong>new</strong> Reset position to start of game but stay in analyze mode.</li>\r
-<li><span class="version1"><strong>setboard</strong> if you have set feature setboard=1; otherwise <strong>edit</strong>. Exiting edit mode returns to analyze mode.</span></li>\r
-<li><strong>exit</strong> Leave analyze mode.</li>\r
-<li><strong>.</strong> Send a search status update (optional); see below.</li>\r
-<li><span class="version1">\r
-<strong>bk</strong> Show book moves from this position,\r
-if any; see above.</span></li>\r
-<li><span class="version1">\r
-<strong>hint</strong> Show the predicted move from this\r
-position, if any; see above.</span></li>\r
-</ul>\r
- \r
-<p>\r
-If the user selects "Periodic Updates", xboard will send the string\r
-".\n" to the chess engine periodically during analyze mode, unless the\r
-last PV received began with a '(' character.\r
-</p>\r
-\r
-<p>\r
-The chess engine should respond to ".\n" with a line like this:\r
-</p>\r
-\r
-<pre>\r
-stat01: time nodes ply mvleft mvtot <span class="version1">mvname</span>\r
-</pre>\r
-\r
-<p>Where:</p>\r
-<table>\r
-<tr><td>time</td><td>Elapsed search time in centiseconds (ie: 567 = 5.67 seconds).</td></tr>\r
-<tr><td>nodes</td><td>Nodes searched so far.</td></tr>\r
-<tr><td>ply</td><td>Search depth so far.</td></tr>\r
-<tr><td>mvleft</td><td>Number of moves left to consider at this depth.</td></tr>\r
-<tr><td>mvtot</td><td>Total number of moves to consider.</td></tr>\r
-<tr class="version1"><td>mvname</td><td>Move currently being considered (SAN or coordinate notation). Optional;\r
-added in protocol version 2.</td></tr>\r
-</table>\r
-\r
-<p>\r
-Examples:\r
-</p>\r
-<pre>\r
- stat01: 1234 30000 7 5 30\r
- stat01: 1234 30000 7 5 30 Nf3\r
-</pre>\r
-\r
-<p>\r
-Meaning:\r
-</p>\r
-\r
-<p>After 12.34 seconds, I've searched 7 ply/30000 nodes, there are a\r
- total of 30 legal moves, and I have 5 more moves to search\r
- before going to depth 8. In the second example, of the 30 legal\r
- moves, the one I am currently searching is Nf3.</p>\r
-\r
-<p>\r
-Implementation of the "." command is optional. If the engine does not\r
-respond to the "." command with a "stat01..." line, xboard will stop\r
-sending "." commands. If the engine does not implement this command,\r
-the analysis window will use a shortened format to display the engine\r
-info.\r
-</p>\r
-\r
-<p>\r
-To give the user some extra information, the chess engine can output\r
-the strings "++\n" and "--\n", to indicate that the current search is\r
-failing high or low, respectively. You don't have to send anything\r
-else to say "Okay, I'm not failing high/low anymore." xboard will\r
-figure this out itself.\r
-</p>\r
-\r
-<h2><a name="13">13. Idioms and backward compatibility features</a></h2>\r
-\r
-<p>\r
-Some engines have variant interpretations of the force/go/white/black,\r
-time/otim, and hard/easy command sets. \r
-In order to accommodate these older engines, xboard uses these commands\r
-only according to the stylized patterns ("idioms") given in this section.\r
-The obsolete white and black commands\r
-have historically been particularly troublesome, and it is recommended\r
-that new engines set the feature colors=0 and/or ignore the commands.\r
-</p>\r
-\r
-<dl>\r
-\r
-<dt>time N</dt>\r
-<dt>otim N</dt>\r
-<dt>MOVE</dt>\r
-<dd>Sent when the opponent makes a move and the engine is already\r
-playing the opposite color.\r
-</dd>\r
-<dt>white</dt>\r
-<dt>go</dt>\r
-<dd>Sent when the engine is in force mode or playing Black but should\r
-switch to playing White. This sequence is sent only when White is\r
-already on move. \r
-<span class="version1">\r
-If you set the feature colors=0, "white" is not sent.\r
-</span>\r
-</dd>\r
-\r
-<dt>black</dt>\r
-<dt>go</dt>\r
-<dd>Sent when the engine is in force mode or playing White but should\r
-switch to playing Black. This sequence is sent only when Black is\r
-already on move. \r
-<span class="version1">\r
-If you set the feature colors=0, "black" is not sent.\r
-</span>\r
-</dd>\r
-\r
-<dt>white</dt>\r
-<dt>time N</dt>\r
-<dt>otim N</dt>\r
-<dt>black</dt>\r
-<dt>go</dt>\r
-<dd>Sent when Black is on move, the engine is in force mode or playing\r
-White, and the engine's clock needs to be updated before it starts\r
-playing. \r
-The initial "white" is a kludge to accommodate GNU Chess\r
-4's variant interpretation of these commands. \r
-<span class="version1">\r
-If you set the feature colors=0, "white" and "black" are not sent.\r
-</span>\r
-</dd>\r
-\r
-<dt>black</dt>\r
-<dt>time N</dt>\r
-<dt>otim N</dt>\r
-<dt>white</dt>\r
-<dt>go</dt>\r
-<dd>Sent when White is on move, the engine is in force mode or playing\r
-Black, and the engine's clock needs to be updated before it starts\r
-playing. See previous idiom. \r
-The initial "black" is a kludge to accommodate GNU Chess\r
-4's variant interpretation of these commands. \r
-<span class="version1">\r
-If you set the feature colors=0, "black" and "white" are not sent.\r
-</span>\r
-</dd>\r
-\r
-<dt>hard</dt>\r
-<dt>easy</dt>\r
-<dd>Sent in sequence to turn off pondering if xboard is not sure\r
-whether it is on. When xboard is sure, it will send "hard" or "easy"\r
-alone. xboard does this because "easy" is a toggle in GNU Chess 4 but\r
-"hard" is an absolute on.\r
-</dd>\r
-</dl>\r
-\r
-<p>\r
-To support older engines, certain additional commands from the engine\r
-to xboard are also recognized. (These are commands by themselves, not\r
-values to be placed in the comment field of the PGN result code.)\r
-These forms are not recommended for new engines; use the PGN result\r
-code commands or the resign command instead.\r
-</p>\r
-\r
-<table>\r
-<tr><th>Command</th> <th>Interpreted as</th></tr>\r
-<tr><td>White resigns </td><td>0-1 {White resigns}</td></tr>\r
-<tr><td>Black resigns </td><td>1-0 {Black resigns}</td></tr>\r
-<tr><td>White </td><td>1-0 {White mates}</td></tr>\r
-<tr><td>Black </td><td>0-1 {Black mates}</td></tr>\r
-<tr><td>Draw </td><td>1/2-1/2 {Draw}</td></tr>\r
-<tr><td>computer mates </td><td>1-0 {White mates} or 0-1 {Black mates}</td></tr>\r
-<tr><td>opponent mates </td><td>1-0 {White mates} or 0-1 {Black mates}</td></tr>\r
-<tr><td>computer resigns </td><td>0-1 {White resigns} or 1-0 {Black resigns}</td></tr>\r
-<tr><td>game is a draw </td><td>1/2-1/2 {Draw}</td></tr>\r
-<tr><td>checkmate </td><td>1-0 {White mates} or 0-1 {Black mates}</td></tr>\r
-</table>\r
-\r
-<p>\r
-Commands in the above table are recognized if they begin a line and\r
-arbitrary characters follow, so (for example) "White mates" will be\r
-recognized as "White", and "game is a draw by the 50 move rule" will\r
-be recognized as "game is a draw". All the commands are\r
-case-sensitive.\r
-</p>\r
-\r
-<p>\r
-An alternative move syntax is also recognized:\r
-</p>\r
-\r
-<table>\r
-<tr><th>Command </th><th>Interpreted as</th></tr>\r
-<tr><td>NUMBER ... MOVE </td><td>move MOVE</td></tr>\r
-</table>\r
-\r
-<p>\r
-Here NUMBER means any string of decimal digits, optionally ending in a\r
-period. MOVE is any string containing no whitespace. In this command\r
-format, xboard requires the "..." even if your engine is playing\r
-White. A command of the form NUMBER MOVE will be ignored. This odd\r
-treatment of the commands is needed for compatibility with gnuchessx.\r
-The original reasons for it are lost in the mists of time, but I\r
-suspect it was originally a bug in the earliest versions of xboard,\r
-before I started working on it, which someone "fixed" in the wrong\r
-way, by creating a special version of gnuchess (gnuchessx) instead of\r
-changing xboard.\r
-</p>\r
-\r
-<p>\r
-Any line that contains the words "offer" and "draw" is recognized as\r
-"offer draw".\r
-</p>\r
-\r
-<p>\r
-The "Illegal move" message is recognized even if spelled "illegal\r
-move" and even if the colon (":") is omitted. This accommodates GNU\r
-Chess 4, which prints messages like "Illegal move (no matching\r
-move)e2e4", and old versions of Crafty, which print just "illegal move".\r
-</p>\r
-\r
-<p>\r
-In Zippy mode, for compatibility with older versions of Crafty,\r
-xboard passes through to ICS any line that begins "kibitz", "whisper",\r
-"tell", or "draw". Do not use this feature in new code. Instead, use the\r
-commands "tellall", "tellothers", "tellopponent", "tellics" (if needed),\r
-"1/2-1/2 {COMMENT}", or "offer draw", as appropriate.\r
-</p>\r
-\r
-<p class="version1">\r
-If the engine responds to the "sd DEPTH" command with an error message\r
-indicating the command is not supported (such as "Illegal move: sd"),\r
-xboard sets an internal flag and subsequently uses the command\r
-"depth\nDEPTH" instead, for the benefit of GNU Chess 4. Note the\r
-newline in the middle of this command! New engines should not rely on\r
-this feature.\r
-</p>\r
-\r
-<p class="version1">\r
-If the engine responds to the "st TIME" command with an error message\r
-indicating the command is not supported (such as "Illegal move: st"),\r
-xboard sets an internal flag and subsequently uses the command "level\r
-1 TIME" instead, for the benefit of GNU Chess 4. Note that this is\r
-not a standard use of the level command, as TIME seconds are not added\r
-after each player makes 1 move; rather, each move is made in at most\r
-TIME seconds. New engines should not implement or rely on this\r
-feature.\r
-</p>\r
-\r
-<div class="version1">\r
-<p>\r
-In support of the -firstHost/-secondHost features, which allow a chess\r
-engine to be run on another machine using the rsh protocol, xboard recognizes\r
-error messages that are likely to come from rsh as fatal errors. The following\r
-messages are currently recognized:\r
-</p>\r
-\r
-<ul>\r
-<li>unknown host</li>\r
-<li>No remote directory</li>\r
-<li>not found</li>\r
-<li>No such file</li>\r
-<li>can't alloc</li>\r
-<li>Permission denied</li>\r
-</ul>\r
-</div>\r
-\r
-<p class="version1">\r
-ChessBase/Fritz now implements the xboard/winboard protocol and can use\r
-WinBoard-compatible engines in its GUI. ChessBase's version of the\r
-protocol is generally the same as version 1, except that they have\r
-added the commands <strong>fritz</strong>, <strong>reset</strong>, and\r
-<strong>ponder</strong>, and the edit subcommands\r
-<strong>castle</strong> and <strong>ep</strong>. If you want your\r
-engine to work well with the ChessBase/Fritz GUI, you may need to\r
-implement these additional commands, and you should also be aware of\r
-the peculiar way that ChessBase uses the protocol. See their <a\r
-href="http://www.chessbase.com/Products/engines/winboard/tech.htm"\r
->web page</a> for documentation.\r
-</p>\r
-\r
-<p class="version1">\r
-ChessMaster 8000 also implements version 1 of the xboard/winboard\r
-protocol and can use WinBoard-compatible engines. The original\r
-release of CM8000 also has one additional restriction: only pure\r
-coordinate notation (e.g., e2e4) is accepted in the move command. A\r
-patch to correct this should be available from The Learning Company\r
-(makers of CM8000) in February 2001.\r
-</p>\r
-<!--#include virtual="/server/footer.html" -->\r
+<!--#include virtual="/server/html5-header.html" -->
+<title>Chess Engine Communication Protocol</title>
+<style type="text/css">
+ .header {
+ border-top:2px solid black;
+ border-bottom:2px solid black;
+ }
+ .version1 { color: red;}
+ .version43 { color: green;}
+ .version44 { color: blue; }
+
+ table tr { text-align: left}
+ tr > td:first-child { font-weight:bold;}
+ dt { font-weight:bold;}
+
+ </style>
+<!--#include virtual="/server/banner.html" -->
+<!--#set var="article_name" value="/server/standards/boilerplate" -->
+<!--#include virtual="/server/gnun/initial-translations-list.html" -->
+
+<div class="header">
+<h1>Chess Engine Communication Protocol</h1>
+<h2><a href="http://www.tim-mann.org/">Tim Mann</a> & <a href="http://home.hccnet.nl/h.g.muller/winboardF.html">H.G.Muller</a></h2>
+<p>
+Version 2; implemented in xboard/WinBoard 4.2.1 and later. (Sept 3, 2009)<br />
+Changes since version 1 are indicated in <span class="version1">red</span>.<br />
+Changes for WinBoard 4.3.xx are indicated in <span class="version43">green</span>.<br />
+Changes for WinBoard 4.4.xx are indicated in <span class="version44">blue</span>.
+</p>
+</div>
+
+<ul>
+<li><a href="#1">1. Introduction</a></li>
+<li><a href="#2">2. Connection</a></li>
+<li><a href="#3">3. Debugging</a></li>
+<li><a href="#4">4. How it got this way</a></li>
+<li><a href="#5">5. WinBoard requires Win32 engines</a></li>
+<li><a href="#6">6. Hints on input/output</a></li>
+<li><a href="#7">7. Signals</a></li>
+<li><a href="#8">8. Commands from xboard to the engine</a></li>
+<li><a href="#9">9. Commands from the engine to xboard</a></li>
+<li><a href="#10">10. Thinking Output</a></li>
+<li><a href="#11">11. Time control</a></li>
+<li><a href="#12">12. Analyze Mode</a></li>
+<li><a href="#13">13. Idioms and backward compatibility features</a></li>
+</ul>
+
+<hr />
+
+<h2><a name="1">1. Introduction</a></h2>
+
+<p>
+This document is a set of rough notes on the protocol that xboard and
+WinBoard use to communicate with gnuchessx and other chess engines.
+These notes may be useful if you want to connect a different chess
+engine to xboard. Throughout the notes, "xboard" means both xboard
+and WinBoard except where they are specifically contrasted.
+</p>
+
+<p>
+There are two reasons I can imagine someone wanting to do this:
+</p>
+
+<ol>
+<li>You have, or are developing, a chess engine but you don't want to
+write your own graphical interface. </li>
+<li>You have, or are developing,a chess engine, and you want to
+interface it to the Internet Chess Server.</li>
+</ol>
+
+<p>
+In case (2), if you are using xboard, you will need to configure the
+"Zippy" code into it, but WinBoard includes this code already. See
+the file <a
+href="http://www.tim-mann.org/xboard/zippy.README">zippy.README</a>
+in the xboard or WinBoard distribution for more information.
+</p>
+
+<p>
+These notes are unpolished, but I've attempted to make them complete
+in this release. If you notice any errors, omissions, or misleading
+statements, let me know.
+</p>
+
+<p>
+I'd like to hear from everyone who is trying to interface their own
+chess engine to xboard/WinBoard. Please join the mailing list for
+authors of xboard/WinBoard compatible chess engines and post a message
+about what you're doing. The list is now hosted by Yahoo Groups; you
+can join at <a href="http://groups.yahoo.com/group/chess-engines"
+>http://groups.yahoo.com/group/chess-engines</a>, or you can read the
+list there without joining. The list is filtered to prevent spam.
+</p>
+
+<p class="version43">
+Note that the WinBoard 4.3.xx line was developed independently of the
+original GNU project, by H.G.Muller.
+If you have questions about WinBoard 4.3.xx, or want to report bugs in it,
+report them in the appropriate section of the
+<a href="http://www.open-aurec.com/wbforum/">WinBoard forum</a>.
+</p>
+
+<h2><a name="2">2. Connection</a></h2>
+
+<p>
+An xboard chess engine runs as a separate process from xboard itself,
+connected to xboard through a pair of anonymous pipes. The engine
+does not have to do anything special to set up these pipes. xboard
+sets up the pipes itself and starts the engine with one pipe as its
+standard input and the other as its standard output. The engine then
+reads commands from its standard input and writes responses to its
+standard output. This is, unfortunately, a little more complicated to
+do right than it sounds; see <a href="#6">section 6</a> below.
+</p>
+
+<p>
+And yes, contrary to some people's expectations, exactly the same
+thing is true for WinBoard. Pipes and standard input/output are
+implemented in Win32 and work fine. You don't have to use DDE, COM,
+DLLs, BSOD, or any of the other infinite complexity that
+Microsoft has created just to talk between two programs. A WinBoard
+chess engine is a Win32 console program that simply reads from its
+standard input and writes to its standard output. See sections
+<a href="#5">5</a> and <a href="#6">6</a> below for additional details.
+</p>
+
+<h2><a name="3">3. Debugging</a></h2>
+
+<p>
+To diagnose problems in your engine's interaction with xboard, use the
+-debug flag on xboard's command line to see the messages that are
+being exchanged. In WinBoard, these messages are written to the file
+WinBoard.debug instead of going to the screen.
+</p>
+
+<p>
+You can turn debug mode on or off while WinBoard is running by
+pressing Ctrl+Alt+F12. You can turn debug mode on or off while xboard
+is running by binding DebugProc to a shortcut key (and pressing the
+key!); see the instructions on shortcut keys in the xboard man page.
+</p>
+
+<p>
+While your engine is running under xboard/WinBoard, you can send a
+command directly to the engine by pressing Shift+1 (xboard) or Alt+1
+(WinBoard 4.0.3 and later). This brings up a dialog that you can type
+your command into. Press Shift+2 (Alt+2) instead to send to the
+second chess engine in Two Machines mode. On WinBoard 4.0.2 and earlier,
+Ctrl+Alt is used in place of Alt; this had to be changed due to a conflict
+with typing the @-sign on some European keyboards.
+</p>
+
+<h2><a name="4">4. How it got this way</a></h2>
+
+<p>
+Originally, xboard was just trying to talk to the existing
+command-line interface of GNU Chess 3.1+ and 4, which was designed
+for people to type commands to. So the communication protocol is very
+ad-hoc. It might have been good to redesign it early on, but because
+xboard and GNU Chess are separate programs, I didn't want to force
+people to upgrade them together to versions that matched. I
+particularly wanted to keep new versions of xboard working with old
+versions of GNU Chess, to make it easier to compare the play of old
+and new gnuchess versions. I didn't foresee the need for a clean
+protocol to be used with other chess engines in the future.
+</p>
+
+<p>
+Circumstances have changed over the years, and now there are many more
+engines that work with xboard. I've had to make the protocol
+description more precise, I've added some features that GNU Chess
+does not support, and I've specified the standard semantics of a few
+features to be slightly different from what GNU Chess 4 does.
+</p>
+
+<p class="version1">
+This release of the protocol specification is the first to carry a
+version number of its own -- version 2. Previous releases simply
+carried a last-modified date and were loosely tied to specific
+releases of xboard and WinBoard. The version number "1" applies
+generally to all those older versions of the protocol.
+</p>
+
+<p class="version1">
+Protocol version 2 remains compatible with older engines but has
+several new capabilities. In particular, it adds the
+"feature" command, a new mechanism for making backward-compatible
+changes and extensions to the protocol. Engines that do not support a
+particular new feature do not have to use it; new features are not
+enabled unless the engine specifically requests them using the feature
+command. If an engine does not send the feature command at all, the
+protocol behavior is nearly identical to version 1. Several new
+features can be selected by the feature command in version 2,
+including the "ping" command (recommended for all engines), the
+"setboard" command, and many optional parameters. Additional features
+will probably be added in future versions.
+</p>
+
+<p class="version43">
+If it is necessary to have a separate name,
+it would be best to refer to the protocol including the green additions as version 2f.
+I really don't think it is a different protocol from version 2, though.
+I just tried to clarify some ambiguities in the original definition,
+now that the WinBoard 4.3.xx line has implemented them in a specific way.
+The hand-shaking protocol for features as defined in protocol 2 perfectly
+allows addition of an occasional new features without any need for stepping up the protocol version number,
+and I think refraining from the latter would enormously lower the barrier for actual
+implementation of these features in engines.
+<br />
+The two really new things are the engine debug comments, and the "nps" command.
+The former merely tries to regulate an extremely common existing pactice
+of having engines dump debug messages on WinBoard in an unprotected way,
+as usually you get away with that.
+</p>
+
+<h2><a name="5">5. WinBoard requires Win32 engines</a></h2>
+
+<p>
+Due to some Microsoft brain damage that I don't understand, WinBoard
+does not work with chess engines that were compiled to use a DOS
+extender for 32-bit addressing. (Probably not with 16-bit DOS or
+Windows programs either.) WinBoard works only with engines that are
+compiled for the Win32 API. You can get a free compiler that targets
+the Win32 API from <a href="http://sources.redhat.com/cygwin/"
+>http://sources.redhat.com/cygwin/</a>. I think DJGPP 2.x should also
+work if you use the RSXNTDJ extension, but I haven't tried it. Of
+course, Microsoft Visual C++ will work. Most likely the other
+commercial products that support Win32 will work too (Borland, etc.),
+but I have not tried them. Delphi has been successfully used to write
+engines for WinBoard; if you want to do this, Tony Werten has donated
+some <a href="http://www.tim-mann.org/winboard/delphi.txt" >sample
+code</a> that should help you get started.
+</p>
+
+<h2><a name="6">6. Hints on input/output</a></h2>
+
+<p>
+Beware of using buffered I/O in your chess engine. The C stdio
+library, C++ streams, and the I/O packages in most other languages use
+buffering both on input and output. That means two things. First,
+when your engine tries to write some characters to xboard, the library
+stashes them in an internal buffer and does not actually write them to
+the pipe connected to xboard until either the buffer fills up or you
+call a special library routine asking for it to be flushed. (In C
+stdio, this routine is named <tt>fflush</tt>.) Second, when your engine tries
+to read some characters from xboard, the library does not read just
+the characters you asked for -- it reads all the characters that are
+currently available (up to some limit) and stashes any characters you
+are not yet ready for in an internal buffer. The next time you ask to
+read, you get the characters from the buffer (if any) before the
+library tries to read more data from the actual pipe.
+</p>
+
+<p>
+Why does this cause problems? First, on the output side, remember
+that your engine produces output in small quantities (say, a few
+characters for a move, or a line or two giving the current analysis),
+and that data always needs to be delivered to xboard/WinBoard for
+display immediately. If you use buffered output, the data you print
+will sit in a buffer in your own address space instead of being
+delivered.
+</p>
+
+<p>
+You can usually fix the output buffering problem by asking for the
+buffering to be turned off. In C stdio, you do this by calling
+<tt>setbuf(stdout, NULL)</tt>. A more laborious and error-prone
+method is to carefully call <tt>fflush(stdout)</tt> after every line
+you output; I don't recommend this. In C++, you can try
+<tt>cout.setf(ios::unitbuf)</tt>, which is documented in current
+editions of "The C++ Programming Language," but not older ones.
+Another C++ method that might work is
+<tt>cout.rdbuf()->setbuf(NULL, 0)</tt>. Alternatively, you can
+carefully call <tt>cout.flush()</tt> after every line you output;
+again, I don't recommend this.
+</p>
+
+<p>
+Another way to fix the problem is to use unbuffered operating system
+calls to write directly to the file descriptor for standard output.
+On Unix, this means <tt>write(1, ...)</tt> -- see the man page for write(2).
+On Win32, you can use either the Unix-like <tt>_write(1, ...)</tt> or Win32
+native routines like <tt>WriteFile</tt>.
+</p>
+
+<p>
+Second, on the input side, you are likely to want to poll during your
+search and stop it if new input has come in. If you implement
+pondering, you'll need this so that pondering stops when the user
+makes a move. You should also poll during normal thinking on your
+move, so that you can implement the "?" (move now) command, and so
+that you can respond promptly to a "result", "force", or "quit"
+command if xboard wants to end the game or terminate your engine.
+Buffered input makes polling more complicated -- when you poll, you
+must stop your search if there are <em>either</em> characters in the buffer
+<em>or</em> characters available from the underlying file descriptor.
+</p>
+
+<p>
+The most direct way to fix this problem is to use unbuffered operating
+system calls to read (and poll) the underlying file descriptor
+directly. On Unix, use <tt>read(0, ...)</tt> to read from standard input, and
+use <tt>select()</tt> to poll it. See the man pages read(2) and select(2).
+(Don't follow the example of GNU Chess 4 and use the FIONREAD ioctl to
+poll for input. It is not very portable; that is, it does not exist
+on all versions of Unix, and is broken on some that do have it.) On
+Win32, you can use either the Unix-like <tt>_read(0, ...)</tt> or the native
+Win32 <tt>ReadFile()</tt> to read. Unfortunately, under Win32, the function to
+use for polling is different depending on whether the input device is
+a pipe, a console, or something else. (More Microsoft brain damage
+here -- did they never hear of device independence?) For pipes, you
+can use <tt>PeekNamedPipe</tt> to poll (even when the pipe is unnamed).
+For consoles,
+you can use <tt>GetNumberOfConsoleInputEvents</tt>. For sockets only, you can
+use <tt>select()</tt>. It might be possible to use
+<tt>WaitForSingleObject</tt> more
+generally, but I have not tried it. Some code to do these things can
+be found in Crafty's utility.c, but I don't guarantee that it's all
+correct or optimal.
+</p>
+
+<p>
+A second way to fix the problem might be to ask your I/O library not
+to buffer on input. It should then be safe to poll the underlying
+file descriptor as described above. With C, you can try calling
+<tt>setbuf(stdin, NULL)</tt>. However, I have never tried this. Also, there
+could be problems if you use <tt>scanf()</tt>, at least with certain patterns,
+because <tt>scanf()</tt> sometimes needs to read one extra character and "push
+it back" into the buffer; hence, there is a one-character pushback
+buffer even if you asked for stdio to be unbuffered. With C++, you
+can try <tt>cin.rdbuf()->setbuf(NULL, 0)</tt>, but again, I have never tried
+this.
+</p>
+
+<p>
+A third way to fix the problem is to check whether there are
+characters in the buffer whenever you poll. C I/O libraries generally
+do not provide any portable way to do this. Under C++, you can use
+<tt>cin.rdbuf()->in_avail()</tt>. This method has been reported to
+work with
+EXchess. Remember that if there are no characters in the buffer, you
+still have to poll the underlying file descriptor too, using the
+method described above.
+</p>
+
+<p>
+A fourth way to fix the problem is to use a separate thread to read
+from stdin. This way works well if you are familiar with thread
+programming. This thread can be blocked waiting for input to come in
+at all times, while the main thread of your engine does its thinking.
+When input arrives, you have the thread put the input into a buffer
+and set a flag in a global variable. Your search routine then
+periodically tests the global variable to see if there is input to
+process, and stops if there is. WinBoard and my Win32 ports of ICC
+timestamp and FICS timeseal use threads to handle multiple input
+sources.
+</p>
+
+<h2><a name="7">7. Signals</a></h2>
+
+<p>Engines that run on Unix need to be concerned with two Unix
+signals: <tt>SIGTERM</tt> and <tt>SIGINT</tt>. This applies both to
+engines that run under xboard and (the unusual case of) engines that
+WinBoard remotely runs on a Unix host using the -firstHost or
+-secondHost feature. It does not apply to engines that run on
+Windows, because Windows does not have Unix-style signals.
+<span class="version1">
+Beginning with version 2, you can now turn off the use of
+either or both
+signals. See the "feature" command in <a href="#6">section 9</a> below.
+</span>
+</p>
+
+<p>First, when an engine is sent the "quit" command, it is also given
+a <tt>SIGTERM</tt> signal shortly afterward to make sure it goes away.
+If your engine reliably responds to "quit", and the signal causes
+problems for you, you should either ignore it by calling
+<tt>signal(SIGTERM, SIG_IGN)</tt> at the start of your program,
+or disable it with the "feature" command.</p>
+
+<p>Second, xboard will send an interrupt signal (<tt>SIGINT</tt>) at
+certain times when it believes the engine may not be listening to user
+input (thinking or pondering). WinBoard currently does this only when
+the engine is running remotely using the -firstHost or -secondHost
+feature, not when it is running locally. You probably need to know
+only enough about this grungy feature to keep it from getting in your
+way.
+</p>
+
+<p>
+The <tt>SIGINT</tt>s are basically tailored to the needs of GNU Chess 4
+on systems where its input polling code is broken or disabled.
+Because they work in a rather peculiar way, it is recommended that you
+either ignore <tt>SIGINT</tt> by having your engine call
+<tt>signal(SIGINT, SIG_IGN)</tt>, or disable it with the "feature"
+command.</p>
+
+<p>
+Here are details for the curious. If xboard needs to send a command
+when it is the chess engine's move (such as before the "?" command),
+it sends a <tt>SIGINT</tt> first. If xboard needs to send commands when it is
+not the chess engine's move, but the chess engine may be pondering
+(thinking on its opponent's time) or analyzing (analysis or analyze
+file mode), xboard sends a <tt>SIGINT</tt> before the first such command only.
+Another <tt>SIGINT</tt> is not sent until another move is made, even if xboard
+issues more commands. This behavior is necessary for GNU Chess 4. The
+first <tt>SIGINT</tt> stops it from pondering until the next move, but on some
+systems, GNU Chess 4 will die if it receives a <tt>SIGINT</tt> when not
+actually thinking or pondering.
+</p>
+
+<p>
+There are two reasons why WinBoard does not send the Win32 equivalent
+of <tt>SIGINT</tt> (which is called <tt>CTRL_C_EVENT</tt>) to local
+engines. First, the Win32 GNU Chess 4 port does not need it. Second, I
+could not find a way to get it to work. Win32 seems to be designed
+under the assumption that only console applications, not windowed
+applications, would ever want to send a <tt>CTRL_C_EVENT</tt>.
+</p>
+
+<h2><a name="8">8. Commands from xboard to the engine</a></h2>
+
+<p>
+All commands from xboard to the engine end with a newline (\n), even
+where that is not explicitly stated. All your output to xboard must
+be in complete lines; any form of prompt or partial line will cause
+problems.
+</p>
+
+<p>
+At the beginning of each game, xboard sends an initialization string.
+This is currently "new\nrandom\n" unless the user changes it with the
+initString or secondInitString option.
+</p>
+
+<p>
+xboard normally reuses the same chess engine process for multiple
+games. At the end of a game, xboard will send the "force" command
+(see below) to make sure your engine stops thinking about the current
+position. It will later send the initString again to start a new
+game. If your engine can't play multiple games, you can disable reuse
+<span class="version1">
+either with the "feature" command (beginning in protocol version
+2; see below) or
+</span>
+with xboard's -xreuse (or -xreuse2) command line
+option. xboard will then ask the process to quit after each game and
+start a new process for the next game.
+</p>
+
+<dl>
+<dt>xboard</dt>
+<dd>This command will be sent once immediately after your engine
+process is started. You can use it to put your engine into "xboard
+mode" if that is needed. If your engine prints a prompt to ask for
+user input, you must turn off the prompt and output a newline when the
+"xboard" command comes in.
+</dd>
+
+<dt class="version1">protover N</dt>
+<dd class="version1">
+<p>Beginning in protocol version 2 (in which N=2), this command will
+be sent immediately after the "xboard" command. If you receive some
+other command immediately after "xboard" (such as "new"), you can
+assume that protocol version 1 is in use. The "protover" command is
+the only new command that xboard always sends in version 2. All other
+new commands to the engine are sent only if the engine first enables
+them with the "feature" command. Protocol versions will always be
+simple integers so that they can easily be compared.
+</p>
+
+<p>Your engine should reply to the protover command by sending the
+"feature" command (see below) with the list of non-default feature
+settings that you require, if any.</p>
+
+<p>Your engine should never refuse to run due to receiving a higher
+protocol version number than it is expecting! New protocol versions
+will always be compatible with older ones by default; the larger
+version number is simply a hint that additional "feature" command
+options added in later protocol versions may be accepted.
+</p>
+</dd>
+
+<dt class="version1">accepted</dt>
+<dt class="version1">rejected</dt>
+<dd class="version1">
+These commands may be sent to your engine in reply to the "feature"
+command; see its documentation below.
+</dd>
+
+<dt>new</dt>
+<dd>Reset the board to the standard chess starting position. Set
+White on move. Leave force mode and set the engine to play Black.
+Associate the engine's clock with Black and the opponent's clock with
+White. Reset clocks and time controls to the start of a new game.
+Use wall clock for time measurement.
+Stop clocks. Do not ponder on this move, even if pondering is on.
+Remove any search depth limit previously set by the sd command.
+</dd>
+
+<dt>variant VARNAME</dt>
+<dd>If the game is not standard chess, but a variant, this command is
+sent after "new" and before the first move or "edit" command. Currently
+defined variant names are:
+
+<table>
+<tr><td>wildcastle</td><td>Shuffle chess where king can castle from d file</td></tr>
+<tr><td>nocastle</td><td>Shuffle chess with no castling at all</td></tr>
+<tr><td>fischerandom</td><td>Fischer Random</td></tr>
+<tr><td>bughouse</td><td>Bughouse, ICC/FICS rules</td></tr>
+<tr><td>crazyhouse</td><td>Crazyhouse, ICC/FICS rules</td></tr>
+<tr><td>losers</td><td>Win by losing all pieces or getting mated (ICC)</td></tr>
+<tr><td>suicide</td><td>Win by losing all pieces including king,
+ or by having fewer pieces when one player has no legal moves (FICS)</td></tr>
+<tr class="version1"><td>giveaway</td><td>Win by losing all pieces including king,
+ or by having no legal moves (ICC)</td></tr>
+<tr><td>twokings</td><td>Weird ICC wild 9</td></tr>
+<tr><td>kriegspiel</td><td>Kriegspiel (engines not supported)</td></tr>
+<tr><td>atomic</td><td>Atomic</td></tr>
+<tr><td>3check</td><td>Win by giving check 3 times</td></tr>
+<tr class="version43"><td>xiangqi </td><td>Chinese Chess (9x10 board)</td></tr>
+<tr class="version43"><td>shogi </td><td>Japanese Chess (9x9 bord)</td></tr>
+<tr class="version43"><td>capablanca</td><td>Capablanca Chess (10x8 board, with Archbishop and Chancellor)</td></tr>
+<tr class="version43"><td>gothic </td><td>Gothic Chess (10x8 board, same with better opening setup)</td></tr>
+<tr class="version43"><td>falcon </td><td>Falcon Chess (10x8 board, with two Falcon pieces)</td></tr>
+<tr class="version43"><td>shatranj </td><td>ancient Arabic Chess, with Elephants and General in stead of B and Q</td></tr>
+<tr class="version43"><td>courier </td><td>Courier Chess (12x8 board, a medieval precursor of modern Chess</td></tr>
+<tr class="version43"><td>knightmate </td><td>King moves as Knight and vice versa</td></tr>
+<tr class="version43"><td>berolina</td><td> Pawns capture straight ahead, and move diagonally</td></tr>
+<tr class="version43"><td>janus</td><td> Janus Chess (10x8, with two Archbishops)</td></tr>
+<tr class="version43"><td>caparandom </td><td>shuffle variant like FRC (10x8 board)</td></tr>
+<tr class="version43"><td>cylinder </td><td>Pieces wrap around between side edges, like board is a cylinder</td></tr>
+<tr class="version44"><td>super </td><td>Superchess: a shuffle variant with 4 fairy pieces on 8x8 board</td></tr>
+<tr class="version44"><td>great </td><td>Great Shatranj: sliders are replaced by corresponding short-range pieces on a 10x8 board</td></tr>
+<tr><td>unknown</td><td>Unknown variant (not supported)</td></tr>
+</table>
+
+</dd>
+
+<dt>quit</dt>
+<dd>The chess engine should immediately exit. This command is used
+when xboard is itself exiting, and also between games if the -xreuse
+command line option is given (or -xreuse2 for the second engine).
+See also <a href="#7">Signals</a> above.
+</dd>
+
+<dt>random</dt>
+<dd>This command is specific to GNU Chess 4. You can either ignore it
+completely (that is, treat it as a no-op) or implement it as GNU Chess
+does. The command toggles "random" mode (that is, it sets random =
+!random). In random mode, the engine adds a small random value to its
+evaluation function to vary its play. The "new" command sets random
+mode off.
+</dd>
+
+<dt>force</dt>
+<dd>Set the engine to play neither color ("force mode"). Stop clocks.
+The engine should check that moves received in force mode are legal
+and made in the proper turn, but should not think, ponder, or make
+moves of its own.
+</dd>
+
+<dt>go</dt>
+<dd>Leave force mode and set the engine to play the color that is on
+move. Associate the engine's clock with the color that is on move,
+the opponent's clock with the color that is not on move. Start the engine's
+clock. Start thinking and eventually make a move.
+</dd>
+
+<dt class="version1">playother</dt>
+<dd class="version1">
+(This command is new in protocol version 2. It is not
+sent unless you enable it with the feature command.)
+Leave force mode and set the engine to play the color that is <i>not</i> on
+move. Associate the opponent's clock with the color that is on move,
+the engine's clock with the color that is not on move. Start the opponent's
+clock. If pondering is enabled, the engine should begin pondering.
+If the engine later receives a move, it should start thinking and eventually
+reply.
+</dd>
+
+<dt>white</dt>
+<dd>
+<p><span class="version1">
+(This command is obsolete as of protocol version 2, but is still
+sent in some situations to accommodate older engines unless you disable it
+with the feature command.)
+</span>
+Set White on move. Set the engine to play Black. Stop clocks.
+</p>
+</dd>
+
+<dt>black </dt>
+<dd>
+<span class="version1">
+(This command is obsolete as of protocol version 2, but is still
+sent in some situations to accommodate older engines unless you disable it
+with the feature command.)
+</span>
+Set Black on move. Set the engine to play White. Stop clocks.
+</dd>
+
+<dt>level MPS BASE INC</dt>
+<dd>Set time controls. See the <a href="#11">Time Control</a> section below.
+</dd>
+
+<dt>st TIME</dt>
+<dd>Set time controls. See the <a href="#11">Time Control</a> section
+below.
+</dd>
+
+<dt>sd DEPTH</dt>
+<dd>
+<p>The engine should limit its thinking to DEPTH ply.
+<span class="version43">The commands "level" or "st" and "sd" can be used together in an orthogonal way.
+If both are issued, the engine should observe both limitations:</span>
+In the protocol, the "sd" command isn't a time control. It doesn't
+say that your engine has unlimited time but must search to exactly the
+given depth. It says that you should pay attention to the time
+control as normal, but cut off the search at the specified depth even
+if you have time to search deeper. If you don't have time to search
+to the specified depth, given your normal time management algorithm,
+then you will want to stop sooner than the given depth.
+</p><p>
+The "new" command should set the search depth back to unlimited. This
+is already stated in the spec. The "level" command should not affect
+the search depth. As it happens, xboard/WinBoard currently always
+sends sd (if needed) right after level, but that isn't part of the
+spec.</p>
+</dd>
+
+<dt><span class="version43">nps NODE_RATE</span></dt>
+<dd><span class="version43">The engine should not use wall-clock time to make its timing decisions,
+but an own internal time measure based on the number of nodes it has searched
+(and will report as "thinking output", see <a href="#10">section 10</a>),
+converted to seconds through dividing by the given NODE_RATE.
+Example: after receiving the commands "st 8" and "nps 10000",
+the engine should never use more that 80,000 nodes in the search for any move.
+In this mode, the engine should report user CPU time used (in its thinking output),
+rather than wall-clock time.
+This even holds if NODE_RATE is given as 0,
+but in that case it should also use the user CPU time for its timing decisions.
+The effect of an "nps" command should persist until the next "new" command.
+</span>
+</dd>
+
+<dt>time N</dt>
+<dd>Set a clock that always belongs to the engine. N is a number in
+ centiseconds (units of 1/100 second). Even if the engine changes to
+ playing the opposite color, this clock remains with the engine.
+</dd>
+
+<dt>otim N</dt>
+
+<dd><p>Set a clock that always belongs to the opponent. N is a number in
+centiseconds (units of 1/100 second). Even if the opponent changes to
+playing the opposite color, this clock remains with the opponent.
+</p><p>
+If needed for purposes of board display in force mode (where the
+engine is not participating in the game) the time clock should be
+associated with the last color that the engine was set to play, the
+otim clock with the opposite color.
+</p>
+<p>
+<span class="version43">This business of "clocks remaining with the engine" is apparently so ambiguous
+that many engines implement it wrong.
+The clocks in fact always remain with the color.
+Which clock reading is relayed with "time", and which by "otim", is determined by which side the engine plays.
+Note that the way the clocks operate and receive extra time (in accordance with the selected time control)
+is not affected in any way by which moves are made by the engine, which by the opponent, and which were forced.
+</span>
+</p>
+<p>
+<span class="version1">
+Beginning in protocol version 2, if you can't handle the time and
+otim commands, you can use the "feature" command to disable them; see
+below.
+</span>
+The following techniques from older protocol versions also
+work: You can ignore the time and otim commands (that is, treat them
+as no-ops), or send back "Error (unknown command): time" the first
+time you see "time".
+</p></dd>
+
+<dt>MOVE</dt>
+<dd>
+<p>See below for the syntax of moves. If the move is illegal, print
+an error message; see the section "<a href="#9">Commands from the engine to
+xboard</a>". If the move is legal and in turn, make it. If not in force
+mode, stop the opponent's clock, start the engine's clock, start
+thinking, and eventually make a move.
+</p><p>
+When xboard sends your engine a move, it normally sends coordinate
+algebraic notation. Examples:
+</p>
+<table>
+<tr><td>Normal moves:</td><td>e2e4</td></tr>
+<tr><td>Pawn promotion:</td><td>e7e8q</td></tr>
+<tr><td>Castling:</td><td>e1g1, e1c1, e8g8, e8c8</td></tr>
+<tr><td>Bughouse/crazyhouse drop:</td><td>P@h3</td></tr>
+<tr><td>ICS Wild 0/1 castling:</td><td>d1f1, d1b1, d8f8, d8b8</td></tr>
+<tr><td>FischerRandom castling:</td><td>O-O, O-O-O (oh, not zero)</td></tr>
+</table>
+
+<p class="version43">
+Note that on boards with more than 9 ranks, counting of the ranks starts at 0.
+</p>
+<p class="version1">
+Beginning in protocol version 2, you can use the feature command
+to select SAN (standard algebraic notation) instead; for example, e4,
+Nf3, exd5, Bxf7+, Qxf7#, e8=Q, O-O, or P@h3. Note that the last form,
+P@h3, is a extension to the PGN standard's definition of SAN, which does
+not support bughouse or crazyhouse.
+</p>
+
+<p>
+xboard doesn't reliably detect illegal moves, because it does not keep
+track of castling unavailability due to king or rook moves, or en
+passant availability. If xboard sends an illegal move, send back an
+error message so that xboard can retract it and inform the user; see
+the section "<a href="#9">Commands from the engine to xboard</a>".
+</p>
+</dd>
+<dt class="version1">usermove MOVE</dt>
+<dd class="version1">
+By default, moves are sent to the engine without a command name;
+the notation is just sent as a line by itself.
+Beginning in protocol version 2, you can use the feature command
+to cause the command name "usermove" to be sent before the move.
+Example: "usermove e2e4".
+</dd>
+
+<dt>?</dt>
+<dd><p>Move now. If your engine is thinking, it should move immediately;
+ otherwise, the command should be ignored (treated as a no-op). It
+ is permissible for your engine to always ignore the ? command. The
+ only bad consequence is that xboard's Move Now menu command will do
+ nothing.
+</p><p>
+It is also permissible for your engine to move immediately if it gets
+any command while thinking, as long as it processes the command right
+after moving, but it's preferable if you don't do this. For example,
+xboard may send post, nopost, easy, hard, force, quit,
+<span class="version1">
+or other commands
+</span>
+while the engine is on move.
+</p>
+</dd>
+
+<dt class="version1">ping N</dt>
+<dd class="version1">
+<p>In this command, N is a decimal number. When you receive the command,
+reply by sending the string <strong>pong N</strong>, where N is the
+same number you received. Important: You must not reply to a "ping"
+command until you have finished executing all commands that you
+received before it. Pondering does not count; if you receive a ping
+while pondering, you should reply immediately and continue pondering.
+Because of the way xboard uses the ping command, if you implement the
+other commands in this protocol, you should never see a "ping" command
+when it is your move; however, if you do, you must not send the "pong"
+reply to xboard until after you send your move. For example, xboard
+may send "?" immediately followed by "ping". If you implement the "?"
+command, you will have moved by the time you see the subsequent ping
+command. Similarly, xboard may send a sequence like "force", "new",
+"ping". You must not send the pong response until after you have
+finished executing the "new" command and are ready for the new game to
+start.
+</p>
+<p>
+The ping command is new in protocol version 2 and will not be sent
+unless you enable it with the "feature" command. Its purpose is to
+allow several race conditions that could occur in previous versions of
+the protocol to be fixed, so it is highly recommended that you
+implement it. It is especially important in simple engines that do
+not ponder and do not poll for input while thinking, but it is needed in all
+engines.
+</p>
+</dd>
+
+<dt>draw</dt>
+<dd>The engine's opponent offers the engine a draw. To accept the
+draw, send "offer draw". To decline, ignore the offer (that is, send
+nothing). If you're playing on ICS, it's possible for the draw offer
+to have been withdrawn by the time you accept it, so don't assume the
+game is over because you accept a draw offer. Continue playing until
+xboard tells you the game is over. See also "offer draw" below.
+</dd>
+
+<dt>result RESULT {COMMENT}</dt>
+<dd>After the end of each game, xboard will send you a result command.
+You can use this command to trigger learning. RESULT is either 1-0,
+0-1, 1/2-1/2, or *, indicating whether white won, black won, the game
+was a draw, or the game was unfinished. The COMMENT string is purely
+a human-readable comment; its content is unspecified and subject to
+change. In ICS mode, it is passed through from ICS uninterpreted.
+Example: <pre>result 1-0 {White mates}</pre>
+<p>
+Here are some notes on interpreting the "result" command. Some apply
+only to playing on ICS ("Zippy" mode).
+</p>
+
+<p>
+If you won but did not just play a mate, your opponent must have
+resigned or forfeited. If you lost but were not just mated, you
+probably forfeited on time, or perhaps the operator resigned manually.
+If there was a draw for some nonobvious reason, perhaps your opponent
+called your flag when he had insufficient mating material (or vice
+versa), or perhaps the operator agreed to a draw manually.
+</p>
+
+<p>
+You will get a result command even if you already know the game ended
+-- for example, after you just checkmated your opponent. In fact, if
+you send the "RESULT {COMMENT}" command (discussed below), you will
+simply get the same thing fed back to you with "result" tacked in
+front. You might not always get a "result *" command, however. In
+particular, you won't get one in local chess engine mode when the user
+stops playing by selecting Reset, Edit Game, Exit or the like.
+</p>
+</dd>
+
+<dt><span class="version1">setboard FEN</span></dt>
+<dd>
+<p><span class="version1">
+The setboard command is the new way to set up positions, beginning
+in protocol version 2. It is not used unless it has been selected
+with the feature command. Here FEN is a position in Forsythe-Edwards
+Notation, as defined in the PGN standard.</span>
+<span class="version43">Note that this PGN standard referred to here
+only applies to normal Chess;
+Obviously in variants that cannot be described by a FEN for normal Chess,
+e.g. because the board is not 8x8, other pieces then PNBRQK participate,
+there are holdings that need to be specified, etc.,
+xboard will use a FEN format that is standard or suitable for that varant.
+In particular, in FRC or CRC, WinBoard will use Shredder-FEN or X-FEN standard,
+i.e. it can use the rook-file indicator letter to represent a castling right
+(like HAha) whenever it wants, but if it uses KQkq, this will always refer
+to the outermost rook on the given side.</span>
+</p>
+
+<p class="version1">
+<em>Illegal positions:</em> Note that either setboard or edit can
+be used to send an illegal position to the engine. The user can
+create any position with xboard's Edit Position command (even, say,
+an empty board, or a board with 64 white kings and no black ones).
+If your engine receives a position that it considers illegal,
+I suggest that you send the response "tellusererror Illegal position",
+and then respond to any attempted move with "Illegal move" until
+the next new, edit, or setboard command.
+</p>
+</dd>
+
+<dt>edit</dt>
+<dd>
+<p><span class="version1">
+The edit command is the old way to set up positions. For compatibility
+with old engines, it is still used by default, but new engines may prefer
+to use the feature command (see below) to cause xboard to use setboard instead.
+</span>
+The edit command puts the chess engine into a special mode, where
+it accepts the following subcommands:</p>
+<table>
+<tr><td>c</td><td>change current piece color, initially white</td></tr>
+<tr><td>Pa4 (for example)</td><td>place pawn of current color on a4</td></tr>
+<tr><td>xa4 (for example)</td><td>empty the square a4 (not used by xboard)</td></tr>
+<tr><td>#</td><td>clear board</td></tr>
+<tr><td>.</td><td>leave edit mode</td></tr>
+</table>
+<p class="version1">
+See the Idioms section below for additional subcommands used in
+ChessBase's implementation of the protocol.
+</p>
+
+<p>The edit command does not change the side to move. To set up a
+black-on-move position, xboard uses the following command sequence:
+</p>
+<pre>
+ new
+ force
+ a2a3
+ edit
+ <edit commands>
+ .
+</pre>
+
+<p>
+This sequence is used to avoid the "black" command, which is now
+considered obsolete and which many engines never did implement as
+specified in this document.
+</p>
+
+<p>
+After an edit command is complete, if a king and a rook are on their
+home squares, castling is assumed to be available to them. En passant
+capture is assumed to be illegal on the current move regardless of the
+positions of the pawns. The clock for the 50 move rule starts at
+zero, and for purposes of the draw by repetition rule, no prior
+positions are deemed to have occurred.
+<span class="version43">
+In FRC or CRC, any rook and king put on the back rank should be considered to
+have castling rights, even if it later becomes apparent that they cannot be both in the
+initial position, because the position just set up is asymmetric.
+It is upto WinBoard to find work-around in cases where this is not desired,
+similar to the "black kludge" shown above, by setting up an earlier position,
+and then do a move to destroy castling rights or create e.p. rights.
+(Don't bet your life on it...)
+</span>
+</p>
+</dd>
+
+<dt>hint</dt>
+<dd>If the user asks for a hint, xboard sends your engine the command
+"hint". Your engine should respond with "Hint: xxx", where xxx is a
+suggested move. If there is no move to suggest, you can ignore the
+hint command (that is, treat it as a no-op).
+</dd>
+
+<dt>bk</dt>
+<dd>If the user selects "Book" from the xboard menu, xboard will send
+your engine the command "bk". You can send any text you like as the
+response, as long as each line begins with a blank space or tab (\t)
+character, and you send an empty line at the end. The text pops up in
+a modal information dialog.
+</dd>
+
+<dt>undo</dt>
+<dd>If the user asks to back up one move, xboard will send you the
+"undo" command. xboard will not send this command without putting you
+in "force" mode first, so you don't have to worry about what should
+happen if the user asks to undo a move your engine made. (GNU Chess 4
+actually switches to playing the opposite color in this case.)
+</dd>
+
+<dt>remove</dt>
+<dd>If the user asks to retract a move, xboard will send you the
+"remove" command. It sends this command only when the user is on
+move. Your engine should undo the last two moves (one for each
+player) and continue playing the same color.
+</dd>
+
+<dt>hard</dt>
+<dd>Turn on pondering (thinking on the opponent's time, also known as
+"permanent brain"). xboard will not make any assumption about what
+your default is for pondering or whether "new" affects this setting.
+</dd>
+
+<dt>easy</dt>
+<dd>Turn off pondering.</dd>
+
+<dt>post</dt>
+<dd>Turn on thinking/pondering output.
+See <a href="#10">Thinking Output</a> section.</dd>
+
+<dt>nopost</dt>
+<dd>Turn off thinking/pondering output.</dd>
+
+<dt>analyze</dt>
+<dd>Enter analyze mode. See <a href="#12">Analyze Mode</a> section.</dd>
+
+<dt>name X </dt>
+<dd>This command informs the engine of its
+opponent's name. When the engine is playing on a chess server, xboard
+obtains the opponent's name from the server.
+<span class="version1">
+When the engine is
+playing locally against a human user, xboard obtains the user's login
+name from the local operating system. When the engine is playing
+locally against another engine, xboard uses either the other engine's
+filename or the name that the other engine supplied in the myname
+option to the feature command. By default, xboard uses the name
+command only when the engine is playing on a chess server. Beginning
+in protocol version 2, you can change this with the name option to the
+feature command; see below.
+</span>
+</dd>
+
+<dt>rating</dt>
+<dd>In ICS mode, xboard obtains the ICS opponent's rating from the
+"Creating:" message that appears before each game. (This message may
+not appear on servers using outdated versions of the FICS code.) In
+Zippy mode, it sends these ratings on to the chess engine using the
+"rating" command. The chess engine's own rating comes first, and if
+either opponent is not rated, his rating is given as 0.
+<span class="version1">
+In the future this command may also be used in other modes, if ratings
+are known.
+</span>
+Example: <pre>rating 2600 1500</pre>
+</dd>
+
+<dt><span class="version1">ics HOSTNAME</span></dt>
+<dd class="version1">
+If HOSTNAME is "-", the engine is playing against a local
+opponent; otherwise, the engine is playing on an Internet Chess Server
+(ICS) with the given hostname. This command is new in protocol
+version 2 and is not sent unless the engine has enabled it with
+the "feature" command. Example: "ics freechess.org"
+</dd>
+
+<dt>computer</dt>
+<dd>The opponent is also a computer chess engine. Some engines alter
+their playing style when they receive this command.
+</dd>
+
+<dt class="version1">pause</dt>
+<dt class="version1">resume</dt>
+<dd class="version1">(These commands are new in protocol
+version 2 and will not be sent unless feature pause=1 is set. At
+this writing, xboard actually does not use the commands at all, but it
+or other interfaces may use them in the future.)
+The "pause" command puts the engine into a special state where it
+does not think, ponder, or otherwise consume significant CPU time.
+The current thinking or pondering (if any) is suspended and both
+player's clocks are stopped. The only command that the interface may
+send to the engine while it is in the paused state is "resume". The
+paused thinking or pondering (if any) resumes from exactly where it
+left off, and the clock of the player on move resumes running from
+where it stopped.
+</dd>
+
+<dt class="version44">memory N</dt>
+<dd class="version44">
+This command informs the engine on how much memory it is allowed to use maximally, in MegaBytes.
+On receipt of this command, the engine should adapt the size of its hash tables accordingly.
+This command does only fix the total memory use,
+the engine has to decide for itself
+(or be configured by the user by other means)
+how to divide up the available memory between the various tables it wants to use
+(e.g. main hash, pawn hash, tablebase cache, bitbases).
+This command will only be sent to engines that have requested it through the memory feature,
+and only at the start of a game,
+as the first of the commands to relay engine option settings just before each "new" command.
+</dd>
+
+<dt class="version44">cores N</dt>
+<dd class="version44">
+This command informs the engine on how many CPU cores it is allowed to use maximally.
+This could be interpreted as the number of search threads for SMP engines.
+(Threads that do not consume significant amounts of CPU time, like I/O threads, need not be included in the count.)
+This command will only be sent to engines that have requested it through the smp feature.
+The engine should be able to respond to the "cores" command any time during a game,
+but it is allowed to finish a search in progress before procesing the command.
+(Obeying the command should take priority over finishing a ponder search, though.)
+In any case it will be sent at the start of every game
+as the last command to relay engine option settings before the "new" command.
+</dd>
+
+<dt class="version44">egtpath TYPE PATH</dt>
+<dd class="version44">
+This command informs the engine in which directory (given by the PATH argument)
+it can find end-game tables of the specified TYPE.
+The TYPE argument can be any character string which does not contain spaces.
+Currently <strong>nalimov</strong> and <strong>scorpio</strong> are defined types,
+for Nalimov tablebases and Scorpio bitbases, respectively,
+but future developers of other formats are free to define their own format names.
+The GUI simply matches the TYPE names the engine says it supports
+with those that the user supplied when configuring xboard.
+For every match, it sends a separate "y" command.
+The PATH argument would normally (for Nalimov) be the pathname of the directory the EGT files are in,
+but could also be the name of a file, or in fact anything the particular EGT type requires.
+It is upto the developer of the EGT format to specify the syntax of this parameter.
+This command will only be sent to engines that have told the GUI they support EGTs of the given TYPE
+through the egt feature.
+It will be sent at the start of each game, before the "new" command.
+</dd>
+
+<dt class="version44">option NAME[=VALUE]</dt>
+<dd class="version44">
+This command changes the setting of the option NAME defined by the engine
+(through an earlier feature command)
+to the given VALUE.
+XBoard will in general have no idea what the option means,
+and will send the command only when a user changes the value of this option through a menu,
+or at startup of the engine
+(before the first 'cores' command or, if that is not sent, the first 'new' command)
+in reaction to command-line options.
+The NAME echoes back to the engine the string that was identified as an option NAME
+in the feature command defining the option.
+The VALUE is of the type (numeric or text or absent) that was implied by the option type
+specified in this feature command,
+i.e. with 'spin' and 'check' options VALUE will be a decimal integer (in the latter case 0 or 1),
+with 'combo' and 'string' options VALUE will be a text string,
+and with 'button' and 'save' options no VALUE will be sent at all.
+</dd>
+</dl>
+
+<h3>Bughouse commands:</h3>
+
+<p>
+xboard now supports bughouse engines when in Zippy mode. See
+<a href="http://www.tim-mann.org/xboard/zippy.README"
+>zippy.README</a> for information on Zippy mode and how to turn on the
+bughouse support. The bughouse move format is given above. xboard
+sends the following additional commands to the engine when in bughouse
+mode.
+Commands to inform your engine of the partner's game state may
+be added in the future.
+</p>
+
+<dl>
+<dt>partner <player></dt>
+<dd><player> is now your partner for future games. Example: <pre>partner mann</pre>
+</dd>
+
+<dt>partner</dt>
+<dd>Meaning: You no longer have a partner.
+</dd>
+
+<dt>ptell <text></dt>
+<dd>Your partner told you <text>, either with a ptell or an ordinary tell.
+</dd>
+
+<dt>holding [<white>] [<black>]</dt>
+<dd>White currently holds <white>; black currently holds <black>.
+ Example: <pre>holding [PPPRQ] []</pre></dd>
+
+<dt>holding [<white>] [<black>] <color><piece></dt>
+<dd>White currently holds <white>; black currently holds <black>, after
+ <color> acquired <piece>. Example: <pre>holding [PPPRQ] [R] BR</pre></dd>
+</dl>
+
+<h2><a name="9">9. Commands from the engine to xboard</a></h2>
+
+<p class="version1">
+In general, an engine should not send any output to xboard that is not
+described in this document. As the protocol is extended, newer
+versions of xboard may recognize additional strings as commands that
+were previously not assigned a meaning.
+</p>
+
+<dl>
+
+<dt class="version1"> feature FEATURE1=VALUE1 FEATURE2=VALUE2 ... </dt>
+<dd class="version1">
+<p>Beginning with version 2, the protocol includes the "feature"
+command, which lets your engine control certain optional protocol
+features. Feature settings are written as FEATURE=VALUE, where
+FEATURE is a name from the list below and VALUE is the value to be
+assigned. Features can take string, integer, or boolean values; the
+type of value is listed for each feature. String values are written
+in double quotes (for example, <tt>feature myname="Miracle Chess
+0.9"</tt>), integers are written in decimal, and boolean values are
+written as 0 for false, 1 for true. Any number of features can be set
+in one feature command, or multiple feature commands can be given.</p>
+
+<p>
+Your engine should send one or more feature commands immediately after
+receiving the "protover" command, since xboard needs to know the
+values of some features before sending further commands to the engine.
+Because engines that predate protocol version 2 do not send "feature",
+xboard uses a timeout mechanism: when it first starts your engine, it
+sends "xboard" and "protover N", then listens for feature commands for
+two seconds before sending any other commands. To end this timeout
+and avoid the wait, set the feature "done=1" at the end of your last
+feature command. To increase the timeout, if needed, set the feature
+"done=0" before your first feature command and "done=1" at the end.
+If needed, it is okay for your engine to set done=0 soon as it starts,
+even before it receives the xboard and protover commands. This can be
+useful if your engine takes a long time to initialize itself. It
+should be harmless even if you are talking to a (version 1) user
+interface that does not understand the "feature" command, since such
+interfaces generally ignore commands from the engine that they do not
+understand.
+</p>
+
+<p>
+The feature command is designed to let the protocol change without
+breaking engines that were written for older protocol versions. When
+a new feature is added to the protocol, its default value is always
+chosen to be compatible with older versions of the protocol that did
+not have the feature. Any feature that your engine does not set in a
+"feature" command retains its default value, so as the protocol
+changes, you do not have to change your engine to keep up with it
+unless you want to take advantage of a new feature. Because some
+features are improvements to the protocol, while others are meant to
+cater to engines that do not implement all the protocol features, the
+recommended setting for a feature is not always the same as the
+default setting. The listing below gives both default and recommended
+settings for most features.
+</p>
+
+<p>
+You may want to code your engine so as to be able to work with
+multiple versions of the engine protocol. Protocol version 1 does not
+send the protover command and does not implement the feature command;
+if you send a feature command in protocol version 1, it will have no
+effect and there will be no response. In protocol version 2 or later,
+each feature F that you set generates the response "accepted F" if the
+feature is implemented, or "rejected F" if it is not. Thus an engine
+author can request any feature without having to keep track of which
+protocol version it was introduced in; you need only check whether the
+feature is accepted or rejected. This mechanism also makes it
+possible for a user interface author to implement a subset of a
+protocol version by rejecting some features that are defined in that
+version; however, you should realize that engine authors are likely to
+code for xboard and may not be prepared to have a feature that they
+depend on be rejected.
+<span class="version44">If the GUI rejects an option feature because of the
+syntax of the value, it should print the value string with the
+"rejected" command, e.g. "rejected option nonsense" in response
+to receiving feature option="nonsense".</span>
+</p>
+
+<p>
+Here are the features that are currently defined.
+</p>
+
+<dl>
+<dt class="version1">ping (boolean, default 0, recommended 1)</dt>
+<dd class="version1">
+If ping=1, xboard may use the protocol's new "ping" command;
+if ping=0, xboard will not use the command.
+</dd>
+
+<dt class="version1">setboard (boolean, default 0, recommended 1)</dt>
+<dd class="version1">
+If setboard=1, xboard will use the protocol's new "setboard" command
+to set up positions; if setboard=0, it will use the older "edit" command.
+</dd>
+
+<dt class="version1">playother (boolean, default 0, recommended 1)</dt>
+<dd class="version1">
+If playother=1, xboard will use the protocol's new "playother" command
+when appropriate; if playother=0, it will not use the command.
+</dd>
+
+<dt class="version1">san (boolean, default 0)</dt>
+<dd class="version1">
+If san=1, xboard will send moves to the engine in standard algebraic
+notation (SAN); for example, Nf3. If san=0, xboard will send moves in
+coordinate notation; for example, g1f3. See MOVE in
+<a href="#8">section 8</a> above for more details of both kinds of notation.
+</dd>
+
+<dt class="version1">usermove (boolean, default 0)</dt>
+<dd class="version1">
+If usermove=1, xboard will send moves to the engine with the
+command "usermove MOVE"; if usermove=0, xboard will send just the move,
+with no command name.
+</dd>
+
+<dt class="version1">time (boolean, default 1, recommended 1)</dt>
+<dd class="version1">
+If time=1, xboard will send the "time" and "otim" commands to
+update the engine's clocks; if time=0, it will not.
+</dd>
+
+<dt class="version1">draw (boolean, default 1, recommended 1)</dt>
+<dd class="version1">
+If draw=1, xboard will send the "draw" command if the engine's opponent
+offers a draw; if draw=0, xboard will not inform the engine about
+draw offers. Note that if draw=1, you may receive a draw offer while you
+are on move; if this will cause you to move immediately, you should set
+draw=0.
+</dd>
+
+<dt class="version1">sigint (boolean, default 1)</dt>
+<dd class="version1">
+If sigint=1, xboard may send SIGINT (the interrupt signal) to
+the engine as <a href="#7">section 7</a> above; if sigint=0, it will
+not.
+</dd>
+
+<dt class="version1">sigterm (boolean, default 1)</dt>
+<dd class="version1">
+If sigterm=1, xboard may send SIGTERM (the termination signal) to
+the engine as <a href="#7">section 7</a> above; if sigterm=0, it will
+not.
+</dd>
+
+<dt class="version1">reuse (boolean, default 1, recommended 1) </dt>
+<dd class="version1">
+If reuse=1, xboard may reuse your engine for multiple games. If
+reuse=0 (or if the user has set the -xreuse option on xboard's command
+line), xboard will kill the engine process after every game and start
+a fresh process for the next game.
+</dd>
+
+<dt class="version1">analyze (boolean, default 1, recommended 1)</dt>
+<dd class="version1">
+If analyze=0, xboard will not try to use the "analyze" command; it
+will pop up an error message if the user asks for analysis mode. If
+analyze=1, xboard will try to use the command if the user asks for
+analysis mode.
+</dd>
+
+<dt class="version1">myname (string, default determined from engine filename)</dt>
+<dd class="version1">
+This feature lets you set the name that xboard will use for your
+engine in window banners, in the PGN tags of saved game files, and when
+sending the "name" command to another engine.
+</dd>
+
+<dt class="version1">variants (string, see text below)</dt>
+<dd><span class="version1">
+This feature indicates which chess variants your engine accepts.
+It should be a comma-separated list of variant names. See the table
+under the "variant" command in <a href="#8">section 8</a> above. If
+you do not set this feature, xboard will assume by default that your
+engine supports all variants. (However, the -zippyVariants
+command-line option still limits which variants will be accepted in
+Zippy mode.) It is recommended that you set this feature to the
+correct value for your engine (just "normal" in most cases) rather
+than leaving the default in place, so that the user will get an
+appropriate error message if he tries to play a variant that your
+engine does not support.</span>
+<br />
+<span class="version43">If your engine can play variants on a deviating board size,
+like capablanca on an 8x8 board, or capablanca crazyhouse,
+it can list them amongst the variants with a prefix spcifying board size plus
+holdings size, like 8x8+0_capablanca or 10x8+7_capablanca.
+If it is capable of playing any variant with an arbitrary board size,
+it should list "boardsize" as one of the variants.
+If there is a maximum to the board size, this can be prefixed,
+e.g. "12x10+0_boardsize".
+</span>
+</dd>
+
+<dt class="version1">colors (boolean, default 1, recommended 0) </dt>
+<dd><span class="version1">
+If colors=1, xboard uses the obsolete "white" and "black"
+commands in a stylized way that works with most older chess engines
+that require the commands. See the "<a href="#13">Idioms</a>" section
+below for details. If colors=0, xboard does not use the "white" and
+"black" commands at all.
+</span>
+</dd>
+
+<dt class="version1">ics (boolean, default 0)</dt>
+<dd class="version1">
+If ics=1, xboard will use the protocol's new "ics" command
+to inform the engine of whether or not it is playing on a chess server;
+if ics=0, it will not.
+</dd>
+
+<dt class="version1">name (boolean, see text below)</dt>
+<dd class="version1">
+If name=1, xboard will use the protocol's "name" command
+to inform the engine of the opponent's name; if name=0, it will not.
+By default, name=1 if the engine is playing on a chess server; name=0 if not.
+</dd>
+
+<dt class="version1">pause (boolean, default 0)</dt>
+<dd class="version1">
+If pause=1, xboard may use the protocol's new "pause" command;
+if pause=0, xboard assumes that the engine does not support this command.
+</dd>
+
+<dt class="version43">nps (boolean, default ?)</dt>
+<dd class="version43">
+If nps=1, it means the engine supports the nps command.
+If nps=0, it means the engine does not support it, and WinBoard should refrain from sending it.
+Default is that WinBoard sends it, in an attempt to try out if the engine understand it.
+The engine should properly respond with "Error (unkown command): nps" if it does not implement it,
+(as any protocol version pre-scribes),
+or WinBoard might assume that the engine did understand the command.
+In that case the use of different time standards that ensues could lead to time forfeits for the engine.
+</dd>
+
+<dt class="version43">debug (boolean, default 0)</dt>
+<dd class="version43">
+If debug=1, it means the engine wants to send debug output prefixed by '#',
+which WinBoard should ignore, except for including it in the winboard.debug file.
+As this feature is added to protocol 2 ony late,
+so that not all protocol-2 supporting versions of WinBoard might implement it,
+it is important that engines check if WinBoard accepts the feature.
+If the feature is rejected,
+engines must refrain from sending the debug output,
+or do so at their own risk.
+</dd>
+
+<dt class="version44">memory (boolean, default 0)</dt>
+<dd class="version44">
+If memory=1, the size of the total amount of memory available for the memory-consuming tables of the engine
+(e.g. hash, EGTB cache)
+will be set by the GUI through the "memory" command.
+</dd>
+
+<dt class="version44">smp (boolean, default 0)</dt>
+<dd class="version44">
+If smp=1, the GUI will send the "cores" command to the engine to inform it how many CPU cores it can use.
+Note that sending smp=1 does not imply the engine can use more than one CPU;
+just that it wants to receive the "cores" command.
+</dd>
+
+<dt class="version44">egt (string, see text below)</dt>
+<dd class="version44">
+This feature indicates which end-game table formats the engine supports.
+It should be a comma-separated list of format names.
+See under the "egtpath" command in <a href="#8">section 8</a> above.
+If you do not set this feature, xboard will assume the engine does not support end-game tables,
+and will not send any "egtpath" commands to inform the engine about their whereabouts.
+</dd>
+
+<dt class="version44">option (string, see text below)</dt>
+<dd><span class="version44">
+This feature is used by the engine to define an option command to appear in a GUI menu,
+so that the user can change the corresponding setting of the engine through the GUI interactively.
+The string describes the option by defining a name, type, current value and (sometimes) the acceptable value range.
+Unlike other features, option features are accumulated by the GUI,
+and the GUI must be able to add a new option to the list at any time,
+even after having received feature done=1.
+There are ten different options types, each requiring a slighly different syntax of the defining string:
+<br />
+feature option="NAME -button"
+<br />
+feature option="NAME -save"
+<br />
+feature option="NAME -reset"
+<br />
+feature option="NAME -check VALUE"
+<br />
+feature option="NAME -string VALUE"
+<br />
+feature option="NAME -spin VALUE MIN MAX"
+<br />
+feature option="NAME -combo CHOICE1 /// CHOICE2 ..."
+<br />
+feature option="NAME -slider VALUE MIN MAX"
+<br />
+feature option="NAME -file VALUE"
+<br />
+feature option="NAME -path VALUE"
+<br />
+NAME is an arbitrary alphanumeric string which can contain spaces;
+the other words in capitals would be replaced by the current (default) setting of the option,
+(a character string for -string options, a decimal number for -spin and -check options,
+were the latter uses 1=checked, 0=unchecked),
+the minimum or maximum value of numeric (-spin) options,
+or arbitrary text labels (for -combo option).
+In the latter case, the current value will be preceded by an asterisk.
+The -file and -path options are similar to -string, but can be used to inform the GUI that
+the text represents a file name or folder name respectively,
+so the GUI dialog could add the appropriate browse button to the text-edit field.
+Similarly, a -slider option is like a -spin, but the GUI might make a different
+graphical representation for it.
+A -save option is like a -button, and defines an immediate command to be sent by the engine.
+With -save the GUI will make sure all current option settings are flushed to the engine
+before it sends this command.
+A -reset option is like a -button, but use of it purges the list of options before sending
+the corresponding option command to the engine.
+This enables the engine to completely redefine its options or their current settings,
+by sending a new set of option feature commands to the GUI,
+terminated by feature done=1.
+(The effect of sending an option feature for an option with the same name as was defined before,
+without first receiving a -reset option command, is undefined.)
+</span>
+</dd>
+
+<dt class="version1">done (integer, no default)</dt>
+<dd><span class="version1">
+If you set done=1 during the initial two-second timeout after
+xboard sends you the "xboard" command, the
+timeout will end and xboard will not look for any more feature
+commands before starting normal operation.
+If you set done=0, the initial timeout is increased to one hour;
+in this case, you must set done=1 before xboard will enter normal operation.
+</span>
+</dd>
+</dl>
+</dd>
+
+
+<dt>Illegal move: MOVE</dt>
+<dt>Illegal move (REASON): MOVE</dt>
+<dd>If your engine receives a MOVE command that is recognizably a move
+but is not legal in the current position, your engine must print an
+error message in one of the above formats so that xboard can pass the
+error on to the user and retract the move. The (REASON) is entirely
+optional. Examples:
+
+<pre>
+ Illegal move: e2e4
+ Illegal move (in check): Nf3
+ Illegal move (moving into check): e1g1
+</pre>
+<p>
+Generally, xboard will never send an ambiguous move, so it does not
+matter whether you respond to such a move with an Illegal move message
+or an Error message.
+</p>
+</dd>
+
+<dt>Error (ERRORTYPE): COMMAND</dt>
+<dd>If your engine receives a command it does not understand or does
+not implement, it should print an error message in the above format so
+that xboard can parse it. Examples:
+<pre>
+ Error (ambiguous move): Nf3
+ Error (unknown command): analyze
+ Error (command not legal now): undo
+ Error (too many parameters): level 1 2 3 4 5 6 7
+</pre>
+</dd>
+
+<dt>move MOVE</dt>
+<dd>Your engine is making the move MOVE. Do not echo moves from
+xboard with this command; send only new moves made by the engine.
+
+<div class="version1">
+<p>For the actual move text from your chess engine (in place of MOVE
+above), your move should be either</p>
+<ul>
+<li>in coordinate notation (e.g.,
+e2e4, e7e8q) with castling indicated by the King's two-square move (e.g.,
+e1g1), or</li>
+<li>in Standard Algebraic Notation (SAN) as defined in the
+Portable Game Notation standard (e.g, e4, Nf3, O-O, cxb5, Nxe4, e8=Q),
+with the extension piece@square (e.g., P@f7) to handle piece placement
+in bughouse and crazyhouse.</li>
+</ul>
+<p>
+xboard itself also accepts some variants of SAN, but for compatibility
+with non-xboard interfaces, it is best not to rely on this behavior.
+</p>
+
+<p>Warning: Even though all versions of this protocol specification
+have indicated that xboard accepts SAN moves, some non-xboard
+interfaces are known to accept only coordinate notation. See the
+Idioms section for more information on the known limitations of some
+non-xboard interfaces. It should be safe to send SAN moves if you
+receive a "protover 2" (or later) command from the interface, but
+otherwise it is best to stick to coordinate notation for maximum
+compatibility. An even more conservative approach would be for your
+engine to send SAN to the interface only if you have set feature san=1
+(which causes the interface to send SAN to you) and have received
+"accepted san" in reply.
+</p>
+</div>
+</dd>
+
+<dt>RESULT {COMMENT}</dt>
+<dd>When your engine detects
+that the game has ended by rule, your engine must output a line of the
+form "RESULT {comment}" (without the quotes), where RESULT is a PGN
+result code (1-0, 0-1, or 1/2-1/2), and comment is the reason. Here
+"by rule" means that the game is definitely over because of what
+happened on the board. In normal chess, this includes checkmate,
+stalemate, triple repetition, the 50 move rule, or insufficient
+material; it does not include loss on time or the like.
+Examples:
+<pre>
+ 0-1 {Black mates}
+ 1-0 {White mates}
+ 1/2-1/2 {Draw by repetition}
+ 1/2-1/2 {Stalemate}
+</pre>
+
+<p>
+xboard relays the result to the user, the ICS, the other engine in Two
+Machines mode, and the PGN save file as required.
+<span class="version43">Note that "definitey over" above means that sending this command
+will be taken by WinBoard as an unconditional refusal of the engine to play on,
+which might cause you to forfeit if the game was in fact not over.
+This command should thus not be used to offer draws, accept draws,
+or make draw-by-rule claims that are not yet valid in the current position
+(but will be after you move).
+For offering and claiming such draws, "offer draw" should be used.</span>
+</p>
+
+<p class="version44">
+Note that (in accordance with FIDE rules) only KK, KNK, KBK and KBKB with all bishops on the
+same color can be claimed as draws on the basis of insufficient mating material.
+The end-games KNNK, KBKN, KNKN and KBKB with unlike bishops do have mate positions,
+and cannot be claimed.
+Complex draws based on locked Pawn chains will not be recognized as draws by most interfaces,
+so do not claim in such positions, but just offer a draw or play on.
+</p>
+
+<p class="version44">
+Note to GUI programmers: RESULT commands that the engine sends immediately after its move
+might be detected by the GUI only after the opponent has moved, because of communication
+and scheduling delays, no matter how fast the engine sent it.
+Any judgement of the validity of RESULT claims based on te "current" board position
+will have to account for this uncertainty.
+</p>
+</dd>
+
+<dt>resign</dt>
+<dd>If your engine wants to resign, it can send the command "resign".
+Alternatively, it can use the "RESULT {comment}" command if the string
+"resign" is included in the comment; for example "0-1 {White
+resigns}". xboard relays the resignation to the user, the ICS, the
+other engine in Two Machines mode, and the PGN save file as required.
+<span class="version44">Note that many interfaces work more smoothly if you resign <em>before</em>
+you move.</span>
+</dd>
+
+<dt>offer draw</dt>
+<dd>If your engine wants to offer a draw by agreement (as opposed to
+claiming a draw by rule), it can send the command "offer draw".
+xboard relays the offer to the user, the ICS, the other engine in Two
+Machines mode, and the PGN save file as required. In Machine White,
+Machine Black, or Two Machines mode, the offer is considered valid
+until your engine has made two more moves.
+<span class="version43">This command must also be used to accept a draw offer.
+Do not use the 1/2-1/2 command for that, as the offer might be no longer valid,
+in which case a refusal to play on implied by the RESULT command might make you forfeit the game.
+"offer draw" should also be used to claim 50-move and 3-fold-repetition draws
+that will occur <em>after</em> your move, by sending it <em>before</em> making the move.
+WinBoard will grant draw offers without the opponent having any say in
+it in situations where draws can be claimed.
+Only if the draw cannot be claimed, the offer will be passed to your opponent after you make your next move,
+just before WinBoard relays this move to the opponent.
+</span>
+</dd>
+
+<dt class="version1">tellopponent MESSAGE</dt>
+<dd class="version1">
+This command lets the engine give a message to its opponent,
+independent of whether the opponent is a user on the local machine or
+a remote ICS user (Zippy mode). MESSAGE consists of any characters,
+including whitespace, to the end of the line. When the engine is
+playing against a user on the local machine, xboard pops up an
+information dialog containing the message. When the engine is playing
+against an opponent on the ICS (Zippy mode), xboard sends "say
+MESSAGE\n" to the ICS.
+</dd>
+
+<dt class="version1">tellothers MESSAGE </dt>
+<dd class="version1">This command lets the engine give a message to people watching the
+game other than the engine's opponent. MESSAGE consists of any
+characters, including whitespace, to the end of the line. When the
+engine is playing against a user on the local machine, this command
+does nothing. When the engine is playing against an opponent on the
+ICS (Zippy mode), xboard sends "whisper MESSAGE\n" to the ICS.
+</dd>
+
+<dt class="version1">tellall MESSAGE</dt>
+<dd class="version1">This command lets the engine give a message to its opponent and
+other people watching the game,
+independent of whether the opponent is a user on the local machine or
+a remote ICS user (Zippy mode). MESSAGE consists of any characters,
+including whitespace, to the end of the line. When the engine is
+playing against a user on the local machine, xboard pops up an
+information dialog containing the message. When the engine is playing
+against an opponent on the ICS (Zippy mode), xboard sends "kibitz
+MESSAGE\n" to the ICS.
+</dd>
+
+<dt>telluser MESSAGE</dt>
+<dd>xboard pops up an information dialog containing the message.
+MESSAGE consists of any characters, including whitespace, to the end
+of the line.
+</dd>
+
+<dt>tellusererror MESSAGE</dt>
+<dd>xboard pops up an error dialog containing the message.
+MESSAGE consists of any characters, including whitespace, to the end
+of the line.
+</dd>
+
+<dt>askuser REPTAG MESSAGE</dt>
+<dd>Here REPTAG is a string containing no whitespace, and MESSAGE
+consists of any characters, including whitespace, to the end of the
+line. xboard pops up a question dialog that says MESSAGE and
+has a typein box. If the user types in "bar", xboard sends "REPTAG
+bar" to the engine. The user can cancel the dialog and send nothing.
+</dd>
+
+<dt>tellics MESSAGE</dt>
+<dd>In Zippy mode, xboard sends "MESSAGE\n" to ICS. MESSAGE consists
+of any characters, including whitespace, to the end of the line.
+</dd>
+
+<dt class="version1">tellicsnoalias MESSAGE</dt>
+<dd class="version1">
+In Zippy mode, xboard sends "xMESSAGE\n" to ICS, where "x" is a
+character that prevents the ICS from expanding command aliases, if
+xboard knows of such a character. (On chessclub.com and chess.net,
+"/" is used; on freechess.org, "$" is used.) MESSAGE consists of any
+characters, including whitespace, to the end of the line.
+</dd>
+
+<dt class="version43"># COMMENT</dt>
+<dd class="version43">
+The engine can send any string of printable characters, terminated by a newline,
+for inclusion in the winboard.debug file, provided the line starts with a '#' character.
+If the engine has set feature debug=1,
+it is guaranteed that WinBoard (and any future version of it) will completely ignore
+these lines in any other respect.
+</dd>
+</dl>
+
+<h2><a name="10">10. Thinking Output</a></h2>
+
+<p>
+If the user asks your engine to "show thinking", xboard sends your
+engine the "post" command. It sends "nopost" to turn thinking off.
+In post mode, your engine sends output lines to show the progress of
+its thinking. The engine can send as many or few of these lines as it
+wants to, whenever it wants to. Typically they would be sent when the
+PV (principal variation) changes or the depth changes. The thinking
+output should be in the following format:
+</p>
+
+<pre>ply score time nodes pv</pre>
+
+<p>Where:</p>
+<table>
+<tr><td>ply</td><td>Integer giving current search depth.</td></tr>
+<tr><td>score</td><td>Integer giving current evaluation in centipawns.</td></tr>
+<tr><td>time</td><td>Current search time in centiseconds (ex:1028 = 10.28 seconds).</td></tr>
+<tr><td>nodes</td><td>Nodes searched.</td></tr>
+<tr><td>pv</td><td>Freeform text giving current "best" line.
+You can continue the pv onto another line if you start each
+continuation line with at least four space characters.</td></tr>
+</table>
+
+<p>
+Example:
+</p>
+
+<pre> 9 156 1084 48000 Nf3 Nc6 Nc3 Nf6</pre>
+
+<p>
+Meaning:
+</p>
+
+<pre>
+9 ply, score=1.56, time = 10.84 seconds, nodes=48000, PV = "Nf3 Nc6 Nc3 Nf6"
+</pre>
+
+<p>
+Longer example from actual Crafty output:
+</p>
+
+<pre>
+ 4 109 14 1435 1. e4 d5 2. Qf3 dxe4 3. Qxe4 Nc6
+ 4 116 23 2252 1. Nf3 Nc6 2. e4 e6
+ 4 116 27 2589 1. Nf3 Nc6 2. e4 e6
+ 5 141 44 4539 1. Nf3 Nc6 2. O-O e5 3. e4
+ 5 141 54 5568 1. Nf3 Nc6 2. O-O e5 3. e4
+</pre>
+
+<p>
+You can use the PV to show other things; for instance, while in book,
+Crafty shows the observed frequency of different reply moves in its
+book. In situations like this where your engine is not really
+searching, start the PV with a '(' character:
+</p>
+
+<pre>
+ 0 0 0 0 (e4 64%, d4 24%)
+</pre>
+
+<p>
+GNU Chess output is very slightly different. The ply number is
+followed by an extra nonblank character, and the time is in seconds,
+not hundredths of seconds. For compatibility, xboard accepts the
+extra character and takes it as a flag indicating the different time
+units. Example:
+</p>
+
+<pre>
+ 2. 14 0 38 d1d2 e8e7
+ 3+ 78 0 65 d1d2 e8e7 d2d3
+ 3& 14 0 89 d1d2 e8e7 d2d3
+ 3& 76 0 191 d1e2 e8e7 e2e3
+ 3. 76 0 215 d1e2 e8e7 e2e3
+ 4& 15 0 366 d1e2 e8e7 e2e3 e7e6
+ 4. 15 0 515 d1e2 e8e7 e2e3 e7e6
+ 5+ 74 0 702 d1e2 f7f5 e2e3 e8e7 e3f4
+ 5& 71 0 1085 d1e2 e8e7 e2e3 e7e6 e3f4
+ 5. 71 0 1669 d1e2 e8e7 e2e3 e7e6 e3f4
+ 6& 48 0 3035 d1e2 e8e7 e2e3 e7e6 e3e4 f7f5 e4d4
+ 6. 48 0 3720 d1e2 e8e7 e2e3 e7e6 e3e4 f7f5 e4d4
+ 7& 48 0 6381 d1e2 e8e7 e2e3 e7e6 e3e4 f7f5 e4d4
+ 7. 48 0 10056 d1e2 e8e7 e2e3 e7e6 e3e4 f7f5 e4d4
+ 8& 66 1 20536 d1e2 e8e7 e2e3 e7e6 e3d4 g7g5 a2a4 f7f5
+ 8. 66 1 24387 d1e2 e8e7 e2e3 e7e6 e3d4 g7g5 a2a4 f7f5
+ 9& 62 2 38886 d1e2 e8e7 e2e3 e7e6 e3d4 h7h5 a2a4 h5h4
+ d4e4
+ 9. 62 4 72578 d1e2 e8e7 e2e3 e7e6 e3d4 h7h5 a2a4 h5h4
+ d4e4
+10& 34 7 135944 d1e2 e8e7 e2e3 e7e6 e3d4 h7h5 c2c4 h5h4
+ d4e4 f7f5 e4f4
+10. 34 9 173474 d1e2 e8e7 e2e3 e7e6 e3d4 h7h5 c2c4 h5h4
+ d4e4 f7f5 e4f4
+</pre>
+
+<p>If your engine is pondering (thinking on its opponent's time) in post
+mode, it can show its thinking then too. In this case your engine may
+omit the hint move (the move it is assuming its opponent will make)
+from the thinking lines <em>if and only if</em> it sends xboard the move in
+the usual "Hint: xxx" format before sending the first line.
+</p>
+
+<h2><a name="11">11. Time control</a></h2>
+
+<p>
+xboard supports three styles of time control: conventional chess clocks,
+the ICS-style incremental clock, and an exact number of seconds per move.
+</p>
+
+<p>In conventional clock mode, every time control period is the same.
+That is, if the time control is 40 moves in 5 minutes, then after each
+side has made 40 moves, they each get an additional 5 minutes, and so
+on, ad infinitum. At some future time it would be nice to support a
+series of distinct time controls. This is very low on my personal
+priority list, but code donations to the xboard project are accepted,
+so feel free to take a swing at it. I suggest you talk to me first,
+though.
+</p>
+
+<p>
+The command to set a conventional time control looks like this:
+</p>
+
+<pre>
+ level 40 5 0
+ level 40 0:30 0
+</pre>
+
+<p>
+The 40 means that there are 40 moves per time control. The 5 means
+there are 5 minutes in the control. In the second example, the 0:30
+means there are 30 seconds. The final 0 means that we are in
+conventional clock mode.
+</p>
+
+<p class="version43">
+Note that the time parameter in this command is not a pure numeric argument,
+but in general is a character string, in order to pass the number of seconds.
+Engines are encouraged to ignore any unexpected characters at the end of this string,
+i.e. following the MIN or MIN:SEC specification.
+Future protocol versions might (under control of an appropriate feature)
+append such extra characters to this argument,
+in order to inform the engine in advance of the time control it can expect after the current session completes.
+E.g. "level 40 25+5 0" could mean that the engine has to play 40 moves in 25 minutes,
+but should expect to get only 5 minutes for the entire remainder of the game after that,
+rather than another 25 minutes for the next 40 moves.
+When the time comes, (i.e. after the 40 moves),
+it will be informed of the time-control change by receiving a new "level 0 5 0" command,
+but engines with advanced time management might want to plan for this in advance.
+</p>
+
+<p>
+The command to set an incremental time control looks like this:
+</p>
+
+<pre>
+ level 0 2 12
+</pre>
+
+<p>
+Here the 0 means "play the whole game in this time control period",
+the 2 means "base=2 minutes", and the 12 means "inc=12 seconds". As
+in conventional clock mode, the second argument to level can be in
+minutes and seconds.
+</p>
+
+<p>
+At the start of the game, each player's clock is set to base minutes.
+Immediately after a player makes a move, inc seconds are added to his
+clock. A player's clock counts down while it is his turn. Your flag
+can be called whenever your clock is zero or negative. (Your clock
+can go negative and then become positive again because of the
+increment.)
+</p>
+
+<p class="version44">
+The number of moves given in the level command (when non-zero) should
+be taken as the number of moves still to do before the specified time
+will be added to the clock, if the "level" command is received after
+some moves have already been played.
+The time given should be interpreted as the time left on its clock
+(including any time left over from the previous sessions),
+and not necessarily the time that will be added to the clock
+after the specified number of moves has been played.
+This is only relevant in WinBoard 4.3.xx, which might send the engine
+"level" commands during a game,
+just before the engine has to start thinking about the first move of
+a new time-control session.
+Example: if at the start of the game "level 40 60 0" was given
+(40 moves per hour),
+and the engine receives "level 20 22 0" just before move 41,
+it should understand that it should do the next 20 moves in 22 minutes
+(pehaps because the secondary session was 20 moves per 15 minutes,
+and it had 7 minutes left on its clock after the first 40 moves).
+</p>
+
+<p>
+A special rule on some ICS implementations: if you ask for a game with
+base=0, the clocks really start at 10 seconds instead of 0. xboard
+itself does not know about this rule, so it passes the 0 on to the
+engine instead of changing it to 0:10.
+</p>
+
+<p>
+ICS also has time odds games. With time odds, each player has his own
+(base, inc) pair, but otherwise things work the same as in normal
+games. The Zippy xboard accepts time odds games but ignores the fact
+that the opponent's parameters are different; this is perhaps not
+quite the right thing to do, but gnuchess doesn't understand time
+odds. Time odds games are always unrated.
+</p>
+
+<p>
+The command to set an exact number of seconds per move looks like this:
+</p>
+
+<pre>
+ st 30
+</pre>
+
+<p>
+This means that each move must be made in at most 30 seconds. Time not used
+on one move does not accumulate for use on later moves.
+</p>
+
+<h2><a name="12">12. Analyze Mode</a></h2>
+
+<p>xboard supports analyzing fresh games, edited positions, and games
+from files. However, all of these look the same from the chess
+engine's perspective. Basically, the engine just has to respond to the
+"analyze" command.
+<span class="version1">
+Beginning in protocol version 2,
+if your engine does not support analyze mode, it should use
+the feature command to set analyze=0.
+</span>
+The older method of
+printing the error message "Error (unknown command): analyze" in
+response to the "analyze" command will also work, however.
+</p>
+
+<p>
+To enter analyze mode, xboard sends the command sequence "post", "analyze".
+Analyze mode in your engine should be
+similar to force mode, except that your engine thinks about what move
+it would make next if it were on move. Your engine should accept the
+following commands while in analyze mode:
+</p>
+
+<ul>
+<li>Any legal move, as in force mode</li>
+<li><strong>undo</strong> Back up one move and analyze previous position.</li>
+<li><strong>new</strong> Reset position to start of game but stay in analyze mode.</li>
+<li><span class="version1"><strong>setboard</strong> if you have set feature setboard=1; otherwise <strong>edit</strong>. Exiting edit mode returns to analyze mode.</span></li>
+<li><strong>exit</strong> Leave analyze mode.</li>
+<li><strong>.</strong> Send a search status update (optional); see below.</li>
+<li><span class="version1">
+<strong>bk</strong> Show book moves from this position,
+if any; see above.</span></li>
+<li><span class="version1">
+<strong>hint</strong> Show the predicted move from this
+position, if any; see above.</span></li>
+</ul>
+
+<p>
+If the user selects "Periodic Updates", xboard will send the string
+".\n" to the chess engine periodically during analyze mode, unless the
+last PV received began with a '(' character.
+</p>
+
+<p>
+The chess engine should respond to ".\n" with a line like this:
+</p>
+
+<pre>
+stat01: time nodes ply mvleft mvtot <span class="version1">mvname</span>
+</pre>
+
+<p>Where:</p>
+<table>
+<tr><td>time</td><td>Elapsed search time in centiseconds (ie: 567 = 5.67 seconds).</td></tr>
+<tr><td>nodes</td><td>Nodes searched so far.</td></tr>
+<tr><td>ply</td><td>Search depth so far.</td></tr>
+<tr><td>mvleft</td><td>Number of moves left to consider at this depth.</td></tr>
+<tr><td>mvtot</td><td>Total number of moves to consider.</td></tr>
+<tr class="version1"><td>mvname</td><td>Move currently being considered (SAN or coordinate notation). Optional;
+added in protocol version 2.</td></tr>
+</table>
+
+<p>
+Examples:
+</p>
+<pre>
+ stat01: 1234 30000 7 5 30
+ stat01: 1234 30000 7 5 30 Nf3
+</pre>
+
+<p>
+Meaning:
+</p>
+
+<p>After 12.34 seconds, I've searched 7 ply/30000 nodes, there are a
+ total of 30 legal moves, and I have 5 more moves to search
+ before going to depth 8. In the second example, of the 30 legal
+ moves, the one I am currently searching is Nf3.</p>
+
+<p>
+Implementation of the "." command is optional. If the engine does not
+respond to the "." command with a "stat01..." line, xboard will stop
+sending "." commands. If the engine does not implement this command,
+the analysis window will use a shortened format to display the engine
+info.
+</p>
+
+<p>
+To give the user some extra information, the chess engine can output
+the strings "++\n" and "--\n", to indicate that the current search is
+failing high or low, respectively. You don't have to send anything
+else to say "Okay, I'm not failing high/low anymore." xboard will
+figure this out itself.
+</p>
+
+<h2><a name="13">13. Idioms and backward compatibility features</a></h2>
+
+<p>
+Some engines have variant interpretations of the force/go/white/black,
+time/otim, and hard/easy command sets.
+In order to accommodate these older engines, xboard uses these commands
+only according to the stylized patterns ("idioms") given in this section.
+The obsolete white and black commands
+have historically been particularly troublesome, and it is recommended
+that new engines set the feature colors=0 and/or ignore the commands.
+</p>
+
+<dl>
+
+<dt>time N</dt>
+<dt>otim N</dt>
+<dt>MOVE</dt>
+<dd>Sent when the opponent makes a move and the engine is already
+playing the opposite color.
+</dd>
+<dt>white</dt>
+<dt>go</dt>
+<dd>Sent when the engine is in force mode or playing Black but should
+switch to playing White. This sequence is sent only when White is
+already on move.
+<span class="version1">
+If you set the feature colors=0, "white" is not sent.
+</span>
+</dd>
+
+<dt>black</dt>
+<dt>go</dt>
+<dd>Sent when the engine is in force mode or playing White but should
+switch to playing Black. This sequence is sent only when Black is
+already on move.
+<span class="version1">
+If you set the feature colors=0, "black" is not sent.
+</span>
+</dd>
+
+<dt>white</dt>
+<dt>time N</dt>
+<dt>otim N</dt>
+<dt>black</dt>
+<dt>go</dt>
+<dd>Sent when Black is on move, the engine is in force mode or playing
+White, and the engine's clock needs to be updated before it starts
+playing.
+The initial "white" is a kludge to accommodate GNU Chess
+4's variant interpretation of these commands.
+<span class="version1">
+If you set the feature colors=0, "white" and "black" are not sent.
+</span>
+</dd>
+
+<dt>black</dt>
+<dt>time N</dt>
+<dt>otim N</dt>
+<dt>white</dt>
+<dt>go</dt>
+<dd>Sent when White is on move, the engine is in force mode or playing
+Black, and the engine's clock needs to be updated before it starts
+playing. See previous idiom.
+The initial "black" is a kludge to accommodate GNU Chess
+4's variant interpretation of these commands.
+<span class="version1">
+If you set the feature colors=0, "black" and "white" are not sent.
+</span>
+</dd>
+
+<dt>hard</dt>
+<dt>easy</dt>
+<dd>Sent in sequence to turn off pondering if xboard is not sure
+whether it is on. When xboard is sure, it will send "hard" or "easy"
+alone. xboard does this because "easy" is a toggle in GNU Chess 4 but
+"hard" is an absolute on.
+</dd>
+</dl>
+
+<p>
+To support older engines, certain additional commands from the engine
+to xboard are also recognized. (These are commands by themselves, not
+values to be placed in the comment field of the PGN result code.)
+These forms are not recommended for new engines; use the PGN result
+code commands or the resign command instead.
+</p>
+
+<table>
+<tr><th>Command</th> <th>Interpreted as</th></tr>
+<tr><td>White resigns </td><td>0-1 {White resigns}</td></tr>
+<tr><td>Black resigns </td><td>1-0 {Black resigns}</td></tr>
+<tr><td>White </td><td>1-0 {White mates}</td></tr>
+<tr><td>Black </td><td>0-1 {Black mates}</td></tr>
+<tr><td>Draw </td><td>1/2-1/2 {Draw}</td></tr>
+<tr><td>computer mates </td><td>1-0 {White mates} or 0-1 {Black mates}</td></tr>
+<tr><td>opponent mates </td><td>1-0 {White mates} or 0-1 {Black mates}</td></tr>
+<tr><td>computer resigns </td><td>0-1 {White resigns} or 1-0 {Black resigns}</td></tr>
+<tr><td>game is a draw </td><td>1/2-1/2 {Draw}</td></tr>
+<tr><td>checkmate </td><td>1-0 {White mates} or 0-1 {Black mates}</td></tr>
+</table>
+
+<p>
+Commands in the above table are recognized if they begin a line and
+arbitrary characters follow, so (for example) "White mates" will be
+recognized as "White", and "game is a draw by the 50 move rule" will
+be recognized as "game is a draw". All the commands are
+case-sensitive.
+</p>
+
+<p>
+An alternative move syntax is also recognized:
+</p>
+
+<table>
+<tr><th>Command </th><th>Interpreted as</th></tr>
+<tr><td>NUMBER ... MOVE </td><td>move MOVE</td></tr>
+</table>
+
+<p>
+Here NUMBER means any string of decimal digits, optionally ending in a
+period. MOVE is any string containing no whitespace. In this command
+format, xboard requires the "..." even if your engine is playing
+White. A command of the form NUMBER MOVE will be ignored. This odd
+treatment of the commands is needed for compatibility with gnuchessx.
+The original reasons for it are lost in the mists of time, but I
+suspect it was originally a bug in the earliest versions of xboard,
+before I started working on it, which someone "fixed" in the wrong
+way, by creating a special version of gnuchess (gnuchessx) instead of
+changing xboard.
+</p>
+
+<p>
+Any line that contains the words "offer" and "draw" is recognized as
+"offer draw".
+</p>
+
+<p>
+The "Illegal move" message is recognized even if spelled "illegal
+move" and even if the colon (":") is omitted. This accommodates GNU
+Chess 4, which prints messages like "Illegal move (no matching
+move)e2e4", and old versions of Crafty, which print just "illegal move".
+</p>
+
+<p>
+In Zippy mode, for compatibility with older versions of Crafty,
+xboard passes through to ICS any line that begins "kibitz", "whisper",
+"tell", or "draw". Do not use this feature in new code. Instead, use the
+commands "tellall", "tellothers", "tellopponent", "tellics" (if needed),
+"1/2-1/2 {COMMENT}", or "offer draw", as appropriate.
+</p>
+
+<p class="version1">
+If the engine responds to the "sd DEPTH" command with an error message
+indicating the command is not supported (such as "Illegal move: sd"),
+xboard sets an internal flag and subsequently uses the command
+"depth\nDEPTH" instead, for the benefit of GNU Chess 4. Note the
+newline in the middle of this command! New engines should not rely on
+this feature.
+</p>
+
+<p class="version1">
+If the engine responds to the "st TIME" command with an error message
+indicating the command is not supported (such as "Illegal move: st"),
+xboard sets an internal flag and subsequently uses the command "level
+1 TIME" instead, for the benefit of GNU Chess 4. Note that this is
+not a standard use of the level command, as TIME seconds are not added
+after each player makes 1 move; rather, each move is made in at most
+TIME seconds. New engines should not implement or rely on this
+feature.
+</p>
+
+<div class="version1">
+<p>
+In support of the -firstHost/-secondHost features, which allow a chess
+engine to be run on another machine using the rsh protocol, xboard recognizes
+error messages that are likely to come from rsh as fatal errors. The following
+messages are currently recognized:
+</p>
+
+<ul>
+<li>unknown host</li>
+<li>No remote directory</li>
+<li>not found</li>
+<li>No such file</li>
+<li>can't alloc</li>
+<li>Permission denied</li>
+</ul>
+</div>
+
+<p class="version1">
+ChessBase/Fritz now implements the xboard/winboard protocol and can use
+WinBoard-compatible engines in its GUI. ChessBase's version of the
+protocol is generally the same as version 1, except that they have
+added the commands <strong>fritz</strong>, <strong>reset</strong>, and
+<strong>ponder</strong>, and the edit subcommands
+<strong>castle</strong> and <strong>ep</strong>. If you want your
+engine to work well with the ChessBase/Fritz GUI, you may need to
+implement these additional commands, and you should also be aware of
+the peculiar way that ChessBase uses the protocol. See their <a
+href="http://www.chessbase.com/Products/engines/winboard/tech.htm"
+>web page</a> for documentation.
+</p>
+
+<p class="version1">
+ChessMaster 8000 also implements version 1 of the xboard/winboard
+protocol and can use WinBoard-compatible engines. The original
+release of CM8000 also has one additional restriction: only pure
+coordinate notation (e.g., e2e4) is accepted in the move command. A
+patch to correct this should be available from The Learning Company
+(makers of CM8000) in February 2001.
+</p>
+</div><!-- for id="content", starts in the include above -->
+<!--#include virtual="/server/footer.html" -->
+<div id="footer">
+
+<p>Please send general FSF & GNU inquiries to
+<a href="mailto:gnu@gnu.org"><gnu@gnu.org></a>.
+There are also <a href="/contact/">other ways to contact</a>
+the FSF.<br />
+Please send broken links and other corrections or suggestions to
+<a href="mailto:bug-xboard@gnu.org"><bug-xboard@gnu.org></a>.</p>
+
+<p>Please see the <a
+href="/server/standards/README.translations.html">Translations
+README</a> for information on coordinating and submitting translations
+of this article.</p>
+
+<p>Copyright © 2009, 2010, 2011, 2012 Free Software Foundation, Inc.</p>
+
+<p>This page is licensed under a <a rel="license"
+href="http://creativecommons.org/licenses/by-nd/3.0/us/">Creative
+Commons Attribution-NoDerivs 3.0 United States License</a>.</p>
+
+<p>Updated:
+<!-- timestamp start -->
+$Date: 2012/01/11 04:39:57 $
+<!-- timestamp end -->
+</p>
+</div>
+</div>
+</body>
+</html>
projects / xboard.git / commitdiff