US and RS characters are much less likely to appear in textual data than Tab or LF.
Also I believe this was the original purpose for US and RS in ASCII. So I'm not sure it is 'weird' to use them for that (although it does seem to be uncommon).
Yeah, it kind of was; also FS and GS. GNU Info files and Babyl files use US that way. Really though you can define whatever weird format you want if you're writing the code for it.
Also I believe this was the original purpose for US and RS in ASCII. So I'm not sure it is 'weird' to use them for that (although it does seem to be uncommon).