Intro
In order to see help text when listing possible completions, you may need to patch your shell. Note that without shell patch, completion works, but only lists possible values without any help text.

What this patch changes?
It adds another SHELL VARIABLE which is passed to completion program upon execution. It is named COMP_TYPE and it's value is the same as current rl_completion_type. It is used to distinguish between first TAB press, when help text musn't be displayed, and subsequent calls, when help text may be displayed and it won't break anything. For possible rl_completion_types see ReadLine library manual. Note that bash, at first attempts '?' completion and then '\t' completion.

Summary
Note that there are now three SHELL VARIABLEs passed to external completion programs: