Never mind, I've decided to implement it differently.  Rather than use Cmark I'll change Next Marked to show EITHER the next error or the next comment.  It's no big deal to skip over the uncommented positions and it has a very nice benefit - while you're playing a game you can mark each position that you'd like to later review regardless of whether a mistake was made.

It seems I may have stirred up some bad memories here.  I apologize for not researching this more carefully before suggesting the "Cmark" flag for displaying commented entries.

For those who would rather forget about Cmarking, I doubt if we need to have a method that allows people to choose between the old and new behavior.  The only case in question is when someone has saved comments for a session and then uses "Go to Next Marked" to review it later.  Would they really be annoyed to not see decisions that weren't worthy of comment?  I think it's safe to say those aren't worth seeing again unless it's a different person reviewing the file.  In that case you could manually select each marked move to see the uncommented positions.

Unconvinced?  The second possibility is to redefine what "Cmarking" means.  I can't find any formal documentation of it, so what if I define it as a way of viewing comments?  Unfortunately the vestiges of the old Cmark will seem confusing.  We would need to remove them and that seems like way too much work.  Plus there may be some people that still use the feature since it does seem valuable.

One last suggestion is to make "Go to Next Cmark" to behave similarly as I suggested for "Go to Next Marked".  If no Cmarked entries exist, display the next comment.  A bit klugy, but maybe practical.  How to document it?  By mentioning some of the history of Cmarking and saying that it now performs double duty.  Or we could just let people do an Internet search for it and find out for themselves.