code: public function enableForm($key = null)
      {
          if (null === $key) {
              $this->activeForms = array_keys($this->forms);
              return $this;
          }
          
          if (!is_array($key)) {
              $key = array($key);
          }
          
          foreach ($key as $k) {
              if (false !== strpos($k, '.')) {
                  // this seems not to be childkey.childform but actualkey.childkey
                  list($childKey, $childForm) = explode('.', $k, 2);
                  $child = $this->getForm($childKey);
                  $child->enableForm($childForm);
              } else {
                  if (isset($this->forms[$k]) && !in_array($k, $this->activeForms)) {
                      $this->activeForms[] = $k;
                  }
              }
          }
          
          return $this;
      }
docs: Enables a formular.
  
  Enabled formulars are included in the {@link getIterator()}
  
  Traverses in child containers through .dot-Notation.
  
  @param string $key
  @return \Core\Form\Container