Hi,
I noticed that this section[1] in the hacking manual mentions:
"This is because Geany depends on GTK 2.8. API symbols from newer GTK/GLib versions should be avoided to keep the source code building against GTK 2.8."
I guess this should be updated to GTK+ 2.12 and to host that version of GTK+ API docs.
[1] http://geany.org/manual/dev/hacking.html#gtk-api-documentation
Cheers, Matthew Brush