.ajaxSubmit excludes the submit field

.ajaxSubmit excludes the submit field

I've looked through the code, and this line is the culprit:

    if (successful && (!n || el.disabled || t == 'reset' || t == 'button' ||
        (t == 'checkbox' || t == 'radio') && !el.checked ||
        (t == 'submit' || t == 'image') && el.form && el.form.clk != el ||
        tag == 'select' && el.selectedIndex == -1)) {
            return null;
    }

The el.form.clk attribute does not exist, for every browser I've tried. The code uses this attribute extensively, and I can see it is intended to append the x,y co-ordinates of the item clicked.

I've checked the most recent code and it's still there [http://malsup.com/jquery/form/]

Is this a normal form attribute? Has it been dropped in recent browsers? Based on the use in the code it looks like it expects every browser to be supporting it.