Version 1.34.0 is available upstream. Please consider updating! It seems that version 1.34.0 is available upstream, while the latest version in the Gentoo tree is 1.33.2-r1. You think this warning is false? Read more about it here.
GTK-Doc is used to document C code.
It is typically used to document the public API of libraries,
such as the GTK+ and GNOME libraries, but it can also be used
to document application code.