public function AddVariable( &$variable )
	{
		$qname = $variable->getQName()->clarkNotation();
		if ( isset( $this->variablesByQName[ $qname ] ) )
		{
			$x = 1;
			\XBRL_Log::getInstance()->formula_validation( "Variable-set", "The variable name (defined on an arc) already exists", array(
				'name' => $qname->clarkNotation(),
				'error' => 'xbrlve:duplicateVariableNames'
			) );
			return false;
		}

		$this->variablesByQName[ $qname ] =& $variable;
		$this->variableLabelToQNameMap[ "{$variable->extendedLinkRoleUri}#{$variable->label}" ] = $qname;

		return true;
	}