github/linguist — pull request #1748 by mrego (2014-11-19 22:10:44+00:00)
Title: Add support for .xht extension which is used in some XHTML files

Some XHTML files use `.xht` extension and they're not being highlighted.

For example:
https://github.com/w3c/csswg-test/blob/master/css-flexbox-1/flex-grow-001.xht