themes documentation

[Rod Butcher <rbutcher hyenainternet com>]

Can somebody point me to technical documentation on how themes work -
hopefully an overview of how / where they're stored (/usr/share/? ), how
changed (settings daemon ? ) & how implemented in apps. I'm trying to
work out what goes on behind the scenes, so I know what to look for when
they don't work or change as advertised.
thanks
Rod