In summary, we’ve seen how six binary elements (the dots) yield 64 possible codes and no more. It just so happens that many of these 64 codes perform double duty depending on their context. Of particular interest is the number indicator and the letter indicator that undoes the number indicator. These codes alter the meaning of the codes that follow them — from letters to numbers and from numbers back to letters. Codes such as these are often called precedence, or shift, codes. They alter the meaning of all subsequent codes until the shift is undone. The capital indicator means that the following letter (and only the following letter) should be uppercase rather than lowercase. A code such as this is known as an escape code. Escape codes let you “escape” from the humdrum, routine interpretation of a sequence of codes and move to a new interpretation.
— Code (Charles Petzold), Loc. 391–7