gentoo-overlay/mate-base/mate-session-manager/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
	<maintainer>
		<email>TomWij@gentoo.org</email>
		<name>Tom Wijsman</name>
	</maintainer>
	<use>
		<flag name="upower">Suspend and hibernate using 
			<pkg>sys-power/upower</pkg>.</flag>
	</use>
</pkgmetadata>