keycap vs keysym

What is the difference please, semantically?

Context, texinfo has @key{PAGEUP} (a label on a key)
but it also has @key{PRIOR} which my keyboard doesn't have.

Which is the more general docbook 4.5 markup please?

regards


-- 
Dave Pawson
XSLT, XSL-FO and Docbook FAQ
http://www.dpawson.co.uk