>> (defvar-keymap expreg-repeat-map
>>    :doc "Repeat map for `expreg' actions."
>>    :repeat '(:hints ((expreg-expand . "expand") (expreg-contract . "contract")))
>>    "\\" 'expreg-expand
>>    "|"  'expreg-contract)
>
> If a hint is missing for a command, it should just have its key mentioned.
> It looks like your idea would require changes to defvar-keymap.  Do you
> want to propose a patch?  We'd need some way to pass the hints in; perhaps
> the macro could set a property on the command symbol as you initially
> proposed.

Alright, let's add this to defvar-keymap.  Please try the following patch.

PS: Do you still think a new custom variable should be added to be able to
disable hint strings?