sys-power/powermgmt-base/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
<use>
    <flag name="pm-utils">Adds support for on_ac_power through <pkg>sys-power/pm-utils</pkg></flag>
  </use>
</pkgmetadata>