$.fn.add(selector) and context

$.fn.add(selector) and context

Using $.fn.add(selector) the context property remains the same.
It's ok, but the given selector will be applied always with the
default context (document).
This is not correct for me if we are using jQuery with xml documents
for example.
$("user", xmlDoc).add("lusers");
There is no way to add lusers of the xmlDoc document!
Here an optional context argument would be useful:
$("user", xmlDoc).add("lusers", xmlDoc);
But even this is not ideal for me. If the context argument is not
given (first example), which document would be used?
I suppose the obvious answer is xmlDoc.
An corrected implementation of add() would be something like this:
jQuery.fn.add = function( selector ) {
return this.pushStack( jQuery.unique( jQuery.merge(
this.get(),
typeof selector === "string" ?
jQuery( selector, (this.context || this[0] ||
0).ownerDocument ) :
jQuery.makeArray( selector )
)));
};
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