Sort out cross-browser incompatibilities in handling of iframe marginwidth/marginheight if only one is set #2486
Description
Consider this testcase:
<iframe src="something" marginwidth="100"></iframe>
Assuming the document at "something" doesn't specify topmargin or marginheight attributes on its <body>, what should the top margin be?
The current behavior in UAs is as follows:
- Blink and WebKit use the default body top margin.
- Edge uses 0 (but uses the default if marginwidth is not specified on the parent
<iframe>). - Gecko has the Blink/WebKit behavior if the framed document is in standards mode and the Edge behavior if the framed document is in quirks mode.