gentoo-overlay/sys-apps/baselayout-prefix/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
	<maintainer type="project">
		<email>prefix@gentoo.org</email>
	</maintainer>
	<use>
		<flag name="prefix-chaining">install in a chained Prefix environment</flag>
	</use>
</pkgmetadata>