avahi won't compile with USE="mono doc". You're missing the depend on >=dev-util/mono-tools-1.1.9 and also it looks like they have the exact same bug as the dbus people have... here's a patch..
Created attachment 76812 [details, diff] avahi-0.6.2-mono-docs.patch
I reported this upstream as well. https://bugs.freedesktop.org/show_bug.cgi?id=5570
*** Bug 118765 has been marked as a duplicate of this bug. ***
still doesn't work in 0.6.3
can we fix this? Simple fix. Simple patch.
Fixed