function getNativeFlags(regex) {
        //return nativ.exec.call(/\/([a-z]*)$/i, String(regex))[1];
        return (regex.global     ? "g" : "") +
               (regex.ignoreCase ? "i" : "") +
               (regex.multiline  ? "m" : "") +
               (regex.extended   ? "x" : "") + // Proposed for ES6, included in AS3
               (regex.sticky     ? "y" : ""); // Proposed for ES6, included in Firefox 3+
    }
Returns native `RegExp` flags used by a regex object.
@private
@param {RegExp} regex Regex to check.
@returns {String} Native flags in use.