Some JQL functions are decidedly non-intuitive, for instance componentsLeadByUser().

Although the suggestions will help you get the right name, it won't show you what it means.

I used some javascript to display the expected argument types and a simple description of the function, but it would be great if this was built-in:

Also if another JQL-function plugin tries to implement something similar most likely they would clash.

Far be it from me to say how it might be implemented, but perhaps with additional info in the jqlfunction section in the plugin xml, or maybe if JqlFunctions implemented some additional interface.