gentoo-overlay/xfce-extra/xfce4-power-manager/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
  <herd>xfce</herd>
  <use>
    <flag name='lxpanel'>Build the applet for <pkg>lxde-base/lxpanel</pkg>, you can set XFCE_PLUGINS="" if you don't want the Xfce dependencies.</flag>
  </use>
</pkgmetadata>