gentoo-overlay/xfce-extra/xfce4-mpc-plugin/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
  <maintainer type="project">
    <email>xfce@gentoo.org</email>
    <name>XFCE Team</name>
  </maintainer>
  <use>
    <flag name="libmpd">Build using <pkg>media-libs/libmpd</pkg> backend, instead of native fallback which is preferred</flag>
  </use>
</pkgmetadata>