I can't see an explicit prohibition in the manual, or in https://orgmode.org/worg/dev/org-syntax.html, but I'm seeing behavior that suggests there perhaps should be, as follows.

So, for vaguely aesthetic reasons, I decided I'd like my TODO keywords to end in colons. That is: TODO:, INPROGRESS:, DONE:, and so on; instead of just TODO, INPROGRESS, DONE, etc. And it seemed to work fine. At very least for things like cycling through sequences, quick selection, color and other face attributes, and so on, there didn't seem to be any issue.

However I've just noticed that the colons do seem to be a problem for smart tree construction. For example, if I run 'C-c / T' and provide "DONE:" (with colon) as the keyword, no headlines are found, despite there being many with that keyword in the relevant file. But if I provide "DONE" (no colon)[1] as the keyword, then all of my "DONE:" (with colon) headlines are found.

As I say, I can't find anything in the documentation saying that colons are forbidden, but it's beginning to feel like it. Does that sound credible, in which case does the documentation need a tweak? Or was there no intention to restrict colon use, in which case is it the sparse tree construction code that needs tweaked?

thanks,

Thomas