In an interview in the "Communications of the ACM" (volume 30, number 4, April 1987), two of the original instruction-set architects — Andris Padegs and Richard Case — weighed in on EDIT and EDIT AND MARK.
The interviewer, Alfred Spector, asked: "Did you ever add instructions to help justify the machine that in retrospect were not really necessary?" Richard Case replied, "Yes. The edit instructions are one clear instance. There are some other examples that are debatable." ED and EDMK sparked intense (and occasionally civil) discussion between CPU engineers, the architecture group, and the languages groups. The result of such discussions is probably why we decided not to enhance these ops with ASCII or UNICODE versions.
