[plt-scheme] SXML vs. X-expressions

Forgive me if this is a FAQ, but what exactly is the relationship
between SXML and PLT's X-expressions?  Are they two competing ways of
doing the same thing, or are there reasons to use both?  I've been
doing XML programming with just (lib "xml.ss" "xml"), but I'm
wondering if I should switch to SXML/SSAX.

--dougo at place.org