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. 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.