private function moveToFirstConcept( $nav, &$contexts, &$units )
	{
		$nav->MoveToDocumentElement();

		$result = $nav->MoveToChild( XPathNodeType::Element );
		while ( $result )
		{
			switch ( $nav->getLocalName() )
			{
				case 'schemaRef':
					break;

				case 'linkbaseRef':
					break;

				case 'context':
					$id = $nav->GetAttribute( 'id', null );
					$contexts[ $id ] = $nav->CloneInstance();
					break;

				case 'unit':
					$id = $nav->GetAttribute( 'id', null );
					$units[ $id ] = $nav->CloneInstance();
					break;

				default:
					// Don't be tempted to chgange this
					return true;
			}

			$result = $nav->MoveToNext( XPathNodeType::Element );
		}

		return false;
	}