If you have a tag like <namespace:customtag></ namespace:customtag> in the test it will silently fail to run.

This is a known limitaion of rasterizeHTML:

HTML elements may only contain colons if the prefix is treated as a namespace and has it declared as it would be in XHTML

However it would be helpful if CSSCritic alerted the user that the DOMParser failed.

The DOMParser is here:

https://github.com/cburgmer/rasterizeHTML.js/blob/dd68b6eb97b6446c17a5b1e2d40cbb1430255638/src/browser.js#L219