Everything old is new again. This reminds me of ZSCII, which was how Infocom games encoded string data to fit ~100kb of text data into a Commodore 64, packing 3 characters into every 2 bytes.

    --first byte-------   --second byte---
    7    6 5 4 3 2  1 0   7 6 5  4 3 2 1 0
    bit  --first--  --second---  --third--

The 5-bit character encoding was one of three character sets:

       Z-char 6789abcdef0123456789abcdef
    current   --------------------------
      A0      abcdefghijklmnopqrstuvwxyz
      A1      ABCDEFGHIJKLMNOPQRSTUVWXYZ
      A2       ^0123456789.,!?_#'"/\-:()
              --------------------------

Z-char 0 was space in all character sets, z-char 1 was newline, z-chars 2 and 3 switched to one of the other character sets depending on which one you were already in for the next character only, and z-chars 4 and 5 switched permanently, the "shift-lock".

https://inform-fiction.org/zmachine/standards/z1point0/sect0...