i would prefer a simple lineedit as with the document class options and would expect people who use this functionality to read the listings documentation.
so i do not see the urgency of validating the input and duplicating the documentation in a separate hints window. we don't do that with the document options either. however, if you want to go there it should be possible implement a qtcompleter that takes care of input between comma's (that separate options) and equal signs. to validate the input use a qvalidator (or maybe you already do that) all this imho of course (and i realize this might be quite a bit of work)
