/**
 * Returns the value of the specified query string parameter.
 * This method is not used internally by the Browser History Manager.
 * However, it is provided here as a helper since many applications
 * using the Browser History Manager will want to read the value of
 * url parameters to initialize themselves.
 *
 * @method getQueryStringParameter
 * @param {string} paramName Name of the parameter we want to look up.
 * @param {string} queryString Optional URL to look at. If not specified,
 *     this method uses the URL in the address bar.
 * @return {string} The value of the specified parameter, or null.
 * @public
 */
function getQueryStringParameter(paramName, url) {

    var i, len, idx, queryString, params, tokens;

    url = url || top.location.href;

    idx = url.indexOf("?");
    queryString = idx >= 0 ? url.substr(idx + 1) : url;

    // Remove the hash if any
    idx = queryString.lastIndexOf("#");
    queryString = idx >= 0 ? queryString.substr(0, idx) : queryString;

    params = queryString.split("&");

    for (i = 0, len = params.length; i < len; i++) {
        tokens = params[i].split("=");
        if (tokens.length >= 2) {
            if (tokens[0] === paramName) {
                return unescape(tokens[1]);
            }
        }
    }

    return null;
}