[mod_python] mod_dav phases question

The apache module 'mod_dav' provides webdav ability to be added to 
<directory>'s.
this provides the usual web_dav calls, one of which is 'PUT'. Apache 
handles put internally,
however we are using mod_dav as part of our CMS, to allow our users to 
'checkout' a document
to a webdav folder and open the file, and we want to capture the put 
phase, so we can take the
newly modified file from the webdav folder and check it back in to our cms.

How can I capture the mod_dav put phase with mod_python?  I was thinking 
an apache filter,
but how can I have that applied only to the mod_dav put phase, rather 
than every request? Is
there some large list somewhere of all the possible phases provided by 
every module I can apply
filters to?

-TJS