gentoo-overlay/games-simulation/train-valley/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "https://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
	<maintainer type="project">
		<email>games@gentoo.org</email>
		<name>Gentoo Games Project</name>
	</maintainer>
	<use>
		<flag name="gui">Install the GUI for configuring screen resolution and input</flag>
	</use>
</pkgmetadata>