One Function To Trap Them All

This is a quick one. This technique could have some side-effect I am not aware about but I've never seen it so far in any library. Talking about LiveMonitor I have successfully tested same concept to create faster implementation of some of my DOM common code, not yet updated in vice-versa.

document.getElementsByClassName Example

(function(childNodes){

/* Another (C) WebReflection Silly Idea */

// how to re-use them all, just an example
if(!document.getElementsByClassName)
    document.getElementsByClassName = function getElementsByClassName(className){
        for(var
            re = new RegExp("(?:\\s|^)" + className + "(?:\\s|$)"),
            ret = [], i = 0, l = 0, length = childNodes.length, node;
            i < length; ++i
        ){
            if((node = childNodes[i]).nodeType === 1 && re.test(node.className))
                ret[l++] = node
            ;
        };
        return ret;
    }
;

// let the magic happen
})(document.getElementsByTagName("*"));

What we have here?

1. A trapped live object, probably used in 90% of selector libraries, but performed via scope resolution (the document) and a function execution (the getElementsByTagName method) over all nodes ("*")
2. a theoretically zero performances impact to retrieve again every node, being live there is no need to refresh it, and being trapped run-time, it will contain few nodes during the first execution
3. a single scope able to create N functions based on one of the most common created HTMLCollection

What do you think?