gentoo-overlay/media-video/aravis/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
  <maintainer type="person">
    <email>lu_zero@gentoo.org</email>
  </maintainer>

  <maintainer type="project">
    <email>media-video@gentoo.org</email>
    <name>Gentoo Video project</name>
  </maintainer>

  <use>
    <flag name="X">
      Build the GTK+-based video viewer for aravis. This requires
      GStreamer and a few plugins but technically not the GST plugin
      for aravis.
    </flag>

    <flag name="gstreamer">
      Build the GStreamer plugin for aravis, but not the video viewer.
    </flag>
  </use>
</pkgmetadata>