Allowed parameters to addtobeamertemplate

Question: How do I get a complete list of the available arguments to addtobeamertemplate?

Background: I want to modify the footline template in the Frankfurt theme. I found some sample code at How to insert page number in Beamer navigation symbols? that looks helpful:

addtobeamertemplate{navigation symbols}{}{%
   usebeamerfont{footline}%
   usebeamercolor[fg]{footline}%
   hspace{1em}%
   insertframenumber/inserttotalframenumber
}

Googling addtobeamertemplate I see other arguments: frametitle, footline, title page. In the Beamer documentation I see frame begin and frame end (p. 63), headline (p. 64), and logo (p. 74).

How do I get a complete list of the available arguments to addtobeamertemplate?