gentoo-overlay/net-misc/apt-cacher-ng/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
<!-- maintainer-needed -->
<use>
<flag name="fuse">Install the <pkg>sys-fs/fuse</pkg> based acngfs, to use a userspace filesystem for the apt cache.</flag>
</use>
</pkgmetadata>