gentoo-overlay/app-text/mathtex/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "https://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
	<!-- maintainer-needed -->
	<use>
		<flag name="png">Generate png images by default instead of gif</flag>
	</use>
	<longdescription>MathTeX parses a LaTeX math expression and immediately emits 
	the corresponding gif (or png) image.  It can be used as cgi program to embed
	LaTeX math in your own html pages, blogs, wikis, etc. Just place an html img
	tag in your document wherever you want to see the corresponding LaTeX
	expression. Take a look at homepage for examples.
	</longdescription>
</pkgmetadata>