China DOS Union

Example:
@echo off&setlocal enabledelayedexpansion
set n=abc987
set "m="
set /p=!n:~-6!<nul
set /p=!m:~0,3!<nul
pause

Here  is the backspace character. I'd like to ask, doesn't set /p=!m:~0,3!<nul mean displaying 3 backspace characters, that is, deleting three characters? In this example, shouldn't the final result be abc? But when I run it, the final result is abc98. I just can't figure it out no matter how much I think about it. Why is that?

Because after this line is output there are still two spaces at the end
set /p=!n:~-6!<nul
Change the above line to
set /p"=!n:~6!!"<nul

I strongly recommend that when you use set in the future, add double quotes whenever possible;
otherwise later on you'll often run into problems with extra spaces or things getting cut off because of spaces;
and you'll often have to waste quite a lot of time looking for this error;
it's best to develop the good habit of adding quotes

Solved, thanks, expert! Added points!