code: public function __isset( $childName )
      {
          // Iterate over all nodes and check if a child with the requested name
          // exists.
          foreach ( $this->nodes as $node )
          {
              if ( isset( $node->$childName ) )
              {
                  // We found something, so that we can immediatly exit with
                  // true. The general count is out of interest here.
                  return true;
              }
          }
  
          // Return false, if no such property could be found before...
          return false;
      }
docs: Check if a property exists
  
  Check if a property given by its name as object property exists. This is
  a quite expensive operation on a node list.
  
  @param string $childName
  @return bool