请教strings.com中的mid使用方法：
STRINGS [目标变量=]MID 源字符串 起止数,终止数
是怎么个用法啊？

F:\WORK\DOS>string help mid

STRINGS 2.5 Copyright 1991-1993, 1995 Douglas Boling
First published in PC Magazine, December 29, 1992

Function: MID - Returns middle n chars.

Syntax: STRINGS [dest var =] MID String, Start char, Length

F:\WORK\DOS>string mid 12345, 1,2
12

F:\WORK\DOS>string mid 12345, 2,2
23

F:\WORK\DOS>string mid 12345, 3,3
345