[eesmith]

Then I'm mixing up my 1960s technology. PLATO supported character composition, and APL used it for operators like ⍋ (∆, backspace, ∣), so I assumed that composition using backspace was a reasonably widely understood concept which would have affected ASCII.

[enf]

I don't know why they were slow to embrace backspace. Maybe just because most of the control character that did make it in came from Teletype's requirements, but the Model 33 couldn't backspace so they didn't ask for that one.