Layouts: xml-style-xsl missing page front-matter value

https://github.com/Phlow/feeling-responsive/blob/gh-pages/_layouts/xml-style.xsl#L7
`<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" {{ page.stylesheetAttributes }}>`
`{{ page.stylesheetAttributes }}`Isn't defined anywhere that I can see?