中国DOS联盟

@echo off
setlocal enabledelayedexpansion
cls
color 0f
title Welcome to CN-DOS!
mode con: cols=30 lines=3
set "a= CN-DOS"
set b=
set "c=12345689abcde"
echo\

:c
for /l %%a in (6,1,28) do (
set /a d=%random%%%13+1
call :pp %%a
)
goto c

:pp
set/p=!a:~-%1!<nul
set/p=!b:~0,%1!<nul
color 0!c:~%d%,1!
goto :eof

哪位高手能帮我解释以下从:c以下的代码??
在线等,谢谢了！！！