It was so-called because it was about 80% of PL/I. Written in PL/I and bootstrapped via the PL/I Optimizing compiler, it was an alternative to PL/S for system programming, compiling initially to an intermediate machine-independent language with symbolic registers and machine-like operations.
It was so-called because it was 80% PL/I. Written in PL/I and bootstrapped using the PL/I Optimizing compiler, it served as an alternative to PL/S for system programming, initially compiling to a machine-independent intermediate language with symbolic registers and operations similar to those of a real machine.