"Heard of", maybe not. But "working with" I can believe. A friend of mine was writing an assembler with a built-in arithmetic expression syntax last year.

Clearly it was low-level, because it wasn't trying to abstract away hardware - but it also wasn't just a straight-up (macro) assembly language, since it provided some specific features that needed a more sophisticated compiler to work properly.

When we speak of low-level coding, almost any abstraction can constitute a huge jump in power from the machine language.