function dump( Lex $Lex, $tab = '' ){
		$tag = $Lex->name( $this->t );
		if( $this->is_terminal() ){
			if( $this->value && $this->value !== $this->t ){
				echo $tab, '<',$tag,">\n   ", $tab, htmlspecialchars($this->value),"\n",$tab,'</',$tag,">\n";
			}
			else {
				echo $tab, htmlspecialchars($this->value),"\n";
			}
		}
		else if( ! $this->length ){
			echo $tab, '<', $tag, " />\n";
		}
		else {
			echo $tab, '<',$tag,">\n";
			foreach( $this->children as $Child ){
				$Child->dump( $Lex, "   ".$tab);
			}
			echo $tab, '</', $tag, ">\n";
		}
	}