ASCII is kinda special in that it's both a way of encoding strings and it has character-to-byte equivalence. You can specify an HTTP header as being any number of characters between `\n\r` characters or any number of bytes between `0x0A 0x0D`, and the parsing code is going to compile to pretty much the same thing regardless of whether you know what `0x0A` means or not.

Right, but to do case-insensitive comparisons of header names you need to decode them as strings, not just byte sequences.