Mail formatting

Unix was the first ASCII-using OS that I saw that used a print control character "\n" as a logical separator. Prior to that, I'd seen decimal 31 (US) used. The benefit of using the ASCII separator characters (US RS GS FS) is that one can stucture a file or files hierarchically (i.e. units in records in groups in files). A shame that our current modern systems don't take advantage of this. Even CDC SCOPE or NOS allowed for file/record-level hierarchies. Up to 15 levels of records were allowed, IIRC. So you could skip to the next level 4 record within a file, bypassing all intervening level 0, 1, 2 and 3 records in the process. A shame that was never carried into our "modern" systems. Does anyone know why SUB (0x1A, 26) was used to denote an EOF in CP/M and, to some extent, DOS text files? IIRC, there is at least one programming language that treats newline as a quotable character. Cheers, Chuck