It seems that people (i.e. implementors) find the use of "window" to mean "top level browsing context" confusing. I think this is because there are already two alternate meanings of the term: "window" the name of the javascript global object, of which there is one per browsing context (top-level or not) and "window" the operating system feature, which may be associated with zero or more top level browsing contexts. In particular an easy mistake to make is to assume that getWindowHandles and similar methods should return one entry per OS window, rather than one per tab.

Given this confusion, I think it would be better to either write out "top level browsing context" explicitly, or invent some new term to mean that. This is just for the text, I presume it isn't reasonable to change the API for compatibility reasons.