gentoo-overlay/app-text/calibre/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
  <maintainer>
    <email>axs@gentoo.org</email>
  </maintainer>
  <maintainer>
    <email>zmedico@gentoo.org</email>
  </maintainer>
  <maintainer>
    <email>yngwin@gentoo.org</email>
  </maintainer>
  <use>
    <flag name="udisks">Add run-time dependency on <pkg>sys-fs/udisks</pkg>
      in order to mount and unmount reading devices.</flag>
  </use>
</pkgmetadata>