TalkChess.com

[H.G.Muller]

Note that another reason for a GUI to want the currmove infos, even if it is fully rule aware, is to use them for ordering moves to present to the user for excluding or including them. So that the most relevant moves can be presented to the user at the beginning of the list. A GUI could be expected to know which moves are legal, but it could never be expected to know which moves are good or relevant.

In WinBoard, for instance, moves from the current position are presented in a header line at the top of the Engine-Output display, so that the user can include or exclude them. There only is room for a limited number of moves, though (and even if there was no such limitation, presenting all 40-50 moves would just make it difficult for the user to locate the move he wants). So you would want the relevant moves to be printed there.

Currently, there is no way WinBoard could know that. So the list starts empty, and you can only exclude the current best move there, by clicking on 'best'. This would from then on write the move that was excluded in the list, and you could go on to exclude the now best move (or other moves, you indicate by playing them on the board), which would also be added, to slowly build the list. But it might be much more convenient to start out with a non-empty list containing the leading moves in the root ordering reported by the engine. Presumably the engine will have some idea which moves are good, because they previously produced fail highs, have a high node count, or whatever, and will order those at the beginning of the list.