xmlto is only required for building with xml-docs. source: (https://gitlab.freedesktop.org/dbus/dbus/-/blob/master/configure.ac) AC_ARG_ENABLE(xml-docs, AS_HELP_STRING([--enable-xml-docs],[build XML documentation (requires xmlto)]),enable_xml_docs=$enableval,enable_xml_docs=auto) Reproducible: Always
marking as major, because app-text/xmlto causes often blockers and questions in support forum.
The doc USE flag really just controls the developer-oriented documentation (doxygen). The xml-docs option controls whether the man pages get built/installed. We enable it unconditionally for that reason.