gentoo-overlay/gnome-base/gdm/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
<herd>gnome</herd>
<use>
	<flag name="fprint">Enables experimental fingerprint authentication using
		<pkg>sys-auth/fprintd</pkg></flag>
	<flag name="plymouth">Enable support for smooth transition from
		<pkg>sys-boot/plymouth</pkg></flag>
</use>
</pkgmetadata>