Source of the idea of using ASCII control characters for markup. I'm not comfortable with using stuff that could be part of the input text, and random Unicode characters are inconvenient, but why not ^V^N and ^V^O for Shift Out and Shift In?

My first sense of enchantment with the nooks and crannies of ASCII came from the U+000E <SO> and U+000F <SI> characters. These were, in the Teletype era, designed to shift the two-color printer ribbon: “out” to red, for emphasis, and then back “in”, to black, for normal text.

ASCII also gifted us this cluster of control characters in its legacy:

• U+001C <FS> - File Separator

• U+001D <GS> - Group Separator

• U+001E <RS> - Record Separator

• U+001F <US> - Unit Separator