gentoo-overlay/app-text/docbook-xsl-stylesheets/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
	<!-- maintainer-needed -->
	<use>
		<flag name="ruby">
			Install the Ruby-based dbtoepub script; requires an interpreter
			compatible with <pkg>app-eselect/eselect-ruby</pkg>.
		</flag>
	</use>
	<upstream>
		<remote-id type="sourceforge">docbook</remote-id>
	</upstream>
</pkgmetadata>