gentoo-overlay/app-misc/ca-certificates/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
<herd>base-system</herd>
<use>
  <flag name='cacert'>
    Include root certs from CAcert (http://www.cacert.org/) and
    Software in the Public Interest (http://www.spi-inc.org/)
  </flag>
</use>
</pkgmetadata>