public function relPath($fp_a, $fp_b)
	{
		$this->debug->groupCollapsed(__CLASS__.'->'.__FUNCTION__);
		#$this->debug->log('fp_a',$fp_a);
		#$this->debug->log('fp_b',$fp_b);
		$cfg = $this->cfg;
		$return = $fp_b;
		$commonDir = $this->commonDir(array($fp_a,$fp_b));
		#$this->debug->log('common_dir',$common_dir);
		if ($commonDir) {
			$a_remain = strlen($commonDir) < strlen($fp_a)
				? substr($fp_a, strlen($commonDir))
				: '';
			$b_remain = strlen($commonDir) < strlen($fp_b)
				? substr($fp_b, strlen($commonDir))
				: '';
			#$this->debug->log('a_remain',$a_remain);
			#$this->debug->log('b_remain',$b_remain);
			$down_path = '.';
			if ($a_remain) {
				$a_is_file		= preg_match('|\.\w{3,4}$|', $a_remain);
				$a_dir_count	= preg_match_all('#[\\\/]#', $a_remain)-1;
				if (!$a_is_file) {
					$a_dir_count++;
				}
				$down_path = '.'.str_repeat($cfg['ds'].'..', $a_dir_count);
			}
			#$this->debug->log('down_path',$down_path);
			$return = $down_path.$b_remain;	// replace backslash with forward-slash
		}
		$return = str_replace($cfg['ds_other'], $cfg['ds'], $return);
		$this->debug->log('return', $return);
		$this->debug->groupEnd();
		return $return;
	}