function splice_at( $i, array $nodes, $len = 0){
		$Child = $this->children[$i];
		$Child->pidx = null;
		$Child->depth = 0;
		array_splice( $this->children, $i, $len, $nodes );
		foreach( $nodes as $Node ){
			$Node->pidx = $this->idx;
		}
		$this->length = count( $this->children );
		$this->p = 0;
		return $Child;
	}