As a concrete example of what you're describing, here's an example of a code used with Linotype typesetting machines: https://archive.org/details/LinotypeHandb

As a concrete example of what you're describing, here's an example of a code used with Linotype typesetting machines: https://archive.org/details/LinotypeHandbookForTeletypesetterOperation1951/page/n18/mode/1up https://archive.org/details/LinotypeHandbookForTeletypesette... This code contains two shift states which map directly to physical Linotype features: 1. Shift and Unshift states map the first 45 codes to the 90 character positions in a standard Linotype magazine. 2. Some Linotype matrices (letter molds) have two font variants (e.g., roman and italic); the UR and LR codes shift between these.