$.fn.add( selector, context )

[rkatic]

1. The optional context will be applied on evolving the selector.

2. If the context argument is not given, then at lest use the same document.

 Discussion

Here the expected implementation:

Query.fn.add = function( selector, context ) {
    return this.pushStack( jQuery.unique( jQuery.merge(
        this.get(),
        typeof selector === "string" ?
            jQuery( selector, context
                || this.context && this.context.ownerDocument || this.context)
                || this[0] && (this[0].ownerDocument || this[0]) ) :
            jQuery.makeArray( selector )
    )));

};

[john]

The more I thought about it, the less sense "

this.context && this.context.ownerDocument" made. The .add() method should use the context specified by the root selector call.

I've implemented this change along with test cases. Thanks for the preliminary patch!  http://github.com/jquery/jquery/commit/b0fe380cf89564305646bbd55d1fd7bd210fd591