Dear All,

I was wondering how many states a checkbox has.
Based on https://orgmode.org/manual/Checkboxes.html I conclude that there
are 3 states:
1. [   ] - not done
2. [ - ] - an intermediate state
3. [X] - done

So I think all 3 states should be available to choose from in the function
'org-columns-next-allowed-value''
for functions that use checkboxes.
In code this is a line
https://git.savannah.gnu.org/cgit/emacs/org-mode.git/tree/lisp/org-colview.el#n754

So I would change it from this:
-      (`(,_ ,_ ,_ ,(or "X" "X/" "X%") ,_) '("[ ]" "[X]")))
to that:
+     (`(,_ ,_ ,_ ,(or "X" "X/" "X%") ,_) '("[ ]" "[-]" "[X]")))

What do you think?

Regards,
Sławomir Grochowski