code: function () {
                      var str, j = i, e;
  
                      if (input.charAt(j) === '~') { j++; e = true; } // Escaped strings
                      if (input.charAt(j) !== '`') { return; }
                      if (env.javascriptEnabled !== undefined && !env.javascriptEnabled) {
                          error("You are using JavaScript, which has been disabled.");
                      }
  
                      if (e) { $char('~'); }
  
                      str = $re(/^`([^`]*)`/);
                      if (str) {
                          return new(tree.JavaScript)(str[1], i, e);
                      }
                  }
docs: JavaScript code to be evaluated  `window.location.href`