[i]frame support

[ziebarthw]

This may already be on the road map. At this phase in the project there seems to virtually no support for content loaded into <[i]frame /> elements.

(perhaps it is blocked by #170 since window.frames would be a significant part of a comprehensive implementation?)

Content on the demo web page delivered via an <iframe src="more-product-details.jsp?id=1234"/></iframe> (inline, JS-generated, etc.) would be missing from the final output.

4.8.5 The iframe element