facebook/rng.io — pull request #59 by SaschaNaz (2013-10-09 05:35:32+00:00)
Title: instanceof HTMLUnknownElement

I think current HTML5 Layout test is not so proper when document.createElement always returns HTMLElement.

document.createElement('abc') instanceof HTMLElement

returns 'true.'
Thus, I fixed it by checking whether it is 'HTMLUnknownElement'