Hi, I'm having difficulties understanding how arguments are being passed to a specific plugin.

The code I borrowed is from Custom jQuery selector for finding usable elements. I embedded the code inside a wrapper fn to reset the focus after some user interaction:

        function setFocus(cont) { // Fired on tab change.
            // Set focus on first usable element within container cont. usable := visible and not disabled.
            $("#"+cont + " input:usable:first").focus();
        };
           
        $.expr[":"].usable = function (node, index, prop, nodes){
            // Find usable elements (i.e. visible and enabled).
            var $node = $(node);        
            return ($node.attr("disabled") !== true) && $node.is(":visible");
        };

The code works fine. I just can't figure out where node, index, etc. are coming from and how they are initialized. Are those args reserved names? Thanks for shedding some light.