code: function url(s) {
    // http://www.w3.org/TR/css3-values/#uris
    // Parentheses, commas, whitespace characters, single quotes (') and double
    // quotes (") appearing in a URI must be escaped with a backslash
    var s2 = s.replace(/(\(|\)|\,|\s|\'|\"|\\)/g, '\\$1');
    // WebKit has a bug when it comes to URLs that end with \
    // https://bugs.webkit.org/show_bug.cgi?id=28885
    if (/\\\\$/.test(s2)) {
      // Add a space to work around the WebKit bug.
      s2 += ' ';
    }
    return 'url("' + s2 + '")';
  }
docs: Generates a CSS url string.
  @param {string} s The URL to generate the CSS url for.
  @return {string} The CSS url string.