[I hope this is the appropriate mailing list for submitting patches]

First of all, thanks for your wonderful work in developing and maintaining
org-mode.

I recently tried to custom-set the value of the
org-agenda-fontify-priorities to get better visual cues from the agenda
view.  I was not able to figure out how to do it by looking from the
org-agenda-fontify-priorities's documentation string alone.

Attached below is a patch for agenda-mode.el (applies against Git master)
with a more detailed description of the assoc list keys.

Cheers,

-- 
Rafael