Overstrike makes ASCII the first multi-byte encoding of an internationalized character set (for the Latin family of scripts anyways).

I'm not kidding. The ASCII character set was actually designed to permit overstriking to yield a variety of characters such as, e.g., á. But of course, this follows from the fact that the typefaces used in typewriters were so designed. Historically that is how people wrote characters like á and ç back in the age of typewriters. This is also why Spanish rules made accents on capital letters optional: it wasn't easy to typeset those on typewriters.

The way to encode á, then, was: a BS ' (a, backspace, apostrophe).

Do I have sources for this? I've lost track of them, and I'm not going to look just now...