[yardshop]

Those are characters " # $ % if you meant decimal codes, and characters 4 5 6 7 if you meant hexadecimal. I would guess you didn't mean either.

Maybe you meant 1 2 3 4 which are SOH STX ETX EOT, which are transmission control codes for serial communications.

Or maybe you meant decimal 28 29 30 31 which are FS GS RS US, which are intended for the purpose of structuring data on magnetic tape.

The problem with those low order characters [0] is typing them and seeing them in editors. It's not impossible to do, but just not commonly done.

0: https://en.wikipedia.org/wiki/Control_character

[chapium]

I'll trade editor awareness of control chars for eliminating the problem in 99.999% of cases.

Also some editors do show the ascii codes, like notepad++.

[jwilk]

Probably meant octal 34–37, i.e. decimal 28–31.