gentoo-overlay/app-emulation/libcacard/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
  <maintainer type="project">
    <email>virtualization@gentoo.org</email>
    <name>Gentoo Virtualization Project</name>
  </maintainer>
  <use>
    <flag name="passthrough">Enable smartcard passthrough support via <pkg>sys-apps/pcsc-lite</pkg></flag>
  </use>
</pkgmetadata>