Spec erroneously limits self-capture to same-document/iframe

[jan-ivar]

There's some evidence this spec is confusing browsing context with top-level browsing context throughout. As a result, the spec's limiting of cropping to elements in the same document that is calling cropTo, appears erroneous:

• In § 4. Scope: "As presently defined, cropTo(ID) returns a rejected Promise if the ID is not associated with an Element within the current browsing context."

The "current browsing context" of a cropTo() call from an iframe is the browsing context local to that iframe only. In contrast, most of the hard discussions I've taken part in in this repo have been around cross-origin serialization of cropTarget, which implies this is not the case. I therefore think fixing this is mostly editorial.

[eladalon1983]

Indeed, the intention was "top level browsing context or any of its descendant browsing contexts."