instanceof HTMLElement in IFRAME is not Element or Object?

Question

Trying determinate DOM Element by simple check

isElement = SomeThing instanceof Element

works in main document, but not on (all?) nodes in

Answer 1

There are different javascript implementations for main document and for iframe documents ???

Yes. The iframe has its own environment with its own globals. Try

var iwin = ifram.contentWindow;
idiv instanceof iwin.HTMLElement; // true
idiv instanceof iwin.Object; // true