Question

TAB, which is pretty convenient way to complete AC suggestions, but in many modes (org, mediawiki-mode) it has been already reserved for another operations. How to teach Emacs use TAB for ac-complete when there are suggestion (line or menu) and for the default major-mode binding otherwise?

Answer 1

I found that the issue was the bindings themselves. AC manual provides the following line:

(define-key ac-completing-map "\t" 'ac-complete)

But if wants to use TAB in a completing map, there is another binding to redefine:

(define-key ac-completing-map (kbd "<tab>") 'ac-complete)

With this line, at first TAB completes the word and then, the second hit of the TAB, do the major mode operation.