var CLASS_NAME = "className",
                BOUNDING_BOX = "boundingBox",
                SKIN_PREFIX = "yui-skin-",
                SKIN_REGEXP = new RegExp("(?:^|\\s)" + SKIN_PREFIX + "(\S+)");

            ...

            getActiveSkin : function() {
                var match;
                this.get(BOUNDING_BOX).ancestor(
                    function(n) {
                        return n.get(CLASS_NAME).match(SKIN_REGEXP);
                    }
                );
                return (match && match[1] || null);
            }