Update description of piece command in protocol specs

diff --git a/engine-intf.html b/engine-intf.html
index 4f4af46..058f147 100644 (file)
--- a/engine-intf.html
+++ b/engine-intf.html
@@ -1591,11 +1591,23 @@ The PIECETOCHAR element would ensure a Bishop would not be accepted as promotion
 </dd>\r
 \r
 <dt><span class="version48">piece ID PIECEDESC</span></dt>\r
-<dd><span class="version48">This command is already reserved for future protocol extension.\r
-The engine can send it in response to a variant command in order to specify that the piece\r
-indicated by its pieceToChar letter ID moves in a non-standard way in this variant.\r
-(This to enable the GUI to reliably perform made detection, and produce good SAN.)\r
-The format of PIECEDESC is subject to future specification.\r
+<dd><span class="version48">The engine can send one or more piece commands\r
+in response to a variant command, in order to specify that the piece\r
+indicated by ID moves in a non-standard way in this variant.\r
+(This to enable the GUI to reliably perform mate detection, and produce good SAN.)\r
+Like in FEN the ID is a case-sensitive letter, specifying the color.\r
+When it is a capital suffixed by &, the description is valid for both colors.\r
+PIECEDESC describes the moves in 'Betza notation',\r
+basically a concatenation of one-letter (upper-case) codes for all of its moves.\r
+These codes can be prefixed with lower-case 'modifiers' to indicate directional sub-sets\r
+(combinations of fblrvs, if the piece is not totally symmetric),\r
+move modality (non-capture, capture, e.p. capture; mce),\r
+and whether the move can jump directly to its destination,\r
+or can be blocked (n).\r
+Moves only valid for a virgin piece are prefixed by 'i'.\r
+An optional numeric suffix on the move indicates the maximum number of times\r
+the move can be repeated in the same direction,\r
+to indicate sliders / riders (with the convention 0 = infinite).\r
 </span>\r
 </dd>\r
 </p>\r