gentoo-overlay/media-sound/sonic-visualiser/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
  <maintainer type="project">
    <email>proaudio@gentoo.org</email>
    <name>Gentoo ProAudio Project</name>
  </maintainer>
  <upstream>
     <remote-id type="github">sonic-visualiser/sonic-visualiser</remote-id>
  </upstream>
  <use>
    <flag name="id3tag">Enables ID3 tagging with id3tag library</flag>
  </use>
</pkgmetadata>