I believe it gets discussed a bit in some Cobol programming texts and ISTR it being discussed in _The Viewport Technician_:

https://www.goodreads.com/book/show/4541460-the-viewport-tec...

Usually though it was a direct display of the program state for a given task, which was part of what made it so efficient --- the task needed to be simplified down into chunks which would fit on/make sense when viewed as text on a text screen viewport.