Optionalnode: string | ElementDetermine the nature of
the argument. If not present, search for the windowId within
document.forms. If present and the value is a
string, assume the string is a DOM id and get the element with
that id and start the search from there. If present and the
value is a DOM element, start the search from there.
The windowId of the current window, or null if the windowId cannot be determined.
Return the windowId of the window in which the argument form is rendered.