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Well, what programmers would have to specify for configuring the Diagram, and what users will finally get to see as a result of that, are completely independent issues. And I am usually a lot less considerate towards programmers than towards users. It is also worthwhile to have a unified method for specifying things, rather than completely different methods for each feature. Irregular promotion zones are already specified in the I.D. through a FEN-like board image, not through a case-label-like list of square coordinates.

What I would want the user to see in a variant with pieces that have location-dependent moves is a piece table with a separate entry for each possible move (so that the user can request move diagrams for each case selectively, by clicking those entries). And the name fields in the table should then get a list of squares where this move applies appended to them. Certain shorthands like a1-h4, or dark/light squares could be used in those lists. The image could be the same for all these entries, or different, as the Diagram's creator thought best. Personally I like to be able to see unambigously how a piece moves from its image, without having to deduce it. So for the Elk Chess Diagram I used a different representation for the Elk on light and dark squares (a Pegasus when it moves like a Knight, a Rook where it moves like a Rook). For Xiangqi I would be inclined to use the same Pawn image on both sides of the River, though.

As for configuring the I.D., I have been experimenting a bit with a new parameter moveMap, embedded between the piece definitions. This can define a FEN of lower-case letters abc..., where a then refers to the preceding piece definition, b to the one before that, etc. This map would than define the morph boards of all the piece entries it refers to. (While the existing morph parameter would define morphing in terms of piece ID rather than sequence in the table, and apply only to a single entry.)

As a shorthand for defining the various moves a piece can have I experimented with the possibility to write a comma-separated list of move descriptors in the field of the piece definition where normally the (single) move descriptor goes. The Diagram script would then automatically expand that to a separate entry for each move in the piece table, with all identical properties except for the move. This would work in cases where you want the piece to be represented by the same image everywhere. This is only useful, though, if the list of squares to which the move applies is appended automatically to the piece name; this cannot be done by hand when the name dield is automatically duplicated. This would require some smartness in the script for recognizing rectangular areas (including files and ranks) or square shades.

Considering that so very few variants would make use of this feature, I wonder if the latter is worthwile...