code: function upgradeDomInternal(optJsClass, optCssClass) {
      if (typeof optJsClass === 'undefined' &&
          typeof optCssClass === 'undefined') {
        for (var i = 0; i < registeredComponents_.length; i++) {
          upgradeDomInternal(registeredComponents_[i].className,
              registeredComponents_[i].cssClass);
        }
      } else {
        var jsClass = /** @type {string} */ (optJsClass);
        if (typeof optCssClass === 'undefined') {
          var registeredClass = findRegisteredClass_(jsClass);
          if (registeredClass) {
            optCssClass = registeredClass.cssClass;
          }
        }
  
        var elements = document.querySelectorAll('.' + optCssClass);
        for (var n = 0; n < elements.length; n++) {
          upgradeElementInternal(elements[n], jsClass);
        }
      }
    }
docs: Searches existing DOM for elements of our component type and upgrades them
  if they have not already been upgraded.
  
  @param {string=} optJsClass the programatic name of the element class we
  need to create a new instance of.
  @param {string=} optCssClass the name of the CSS class elements of this
  type will have.