docs: function refresh($target) {
                  var PREFIX = ["-webkit-", ""];
                  var valid = function (prop) {
                      return (prop && "none" !== prop);
                  };
                  var dataUrl;
                  for (var i = 0, n = PREFIX.length; i < n; i++) {
                      if (!valid(dataUrl)) {
                          dataUrl = $target.css(PREFIX[i] + "mask-image");
                          if (valid(dataUrl)) {
                              // iOS では url(data***); 内に '"' は入らない
                              var match = dataUrl.match(/(url\(data:image\/svg\+xml;)([\s\S]*)?(base64,[\s\S]*\))/);
                              if (match) {
                                  dataUrl = match[1] + "bust=" + Date.now().toString(36) + ";" + match[3];
                              }
                              else {
                                  dataUrl = null;
                              }
                          }
                      }
                      if (valid(dataUrl)) {
                          $target.css(PREFIX[i] + "mask-image", dataUrl);
                      }
                  }
                  return $target;
              }