Getting the revisions of .hgtags programatically

[Roy Marples]

Hi List

I'm working on added tag support to the fastexport extension.
I have little idea about the internals of mercurial so asking here for guidance.

My idea is to walk the revisions of .hgtags backwards until I find a changeset 
which added the tag name.
Once found I can export the user, date and message into the fastexport.

What is the best way of achieving this please?
I am currently looking at the annotate code as that gets what I want, but it's 
slow going working it all out and would appreciate somem guidance if possible.

Please include me directly in replies as I'm not subbed to this list.
Thanks

Roy