>They may be some kind of quoted text - long compiler error messages, oops reports, whatever. Things that have a certain specific format.
In the contexts where it matters, the display software can mark each linebreak it inserts with a special symbol that's not found in plain text (possible even in terminal apps, e.g. by using inverted color) to indicate it wasn't found in the original text. Unlike pre-formatting text, this does not lose information.
It's a method of displaying plain text that distinguishes between original linebreaks and linebreaks inserted by the display software. The text itself is 100% plain.
In the contexts where it matters, the display software can mark each linebreak it inserts with a special symbol that's not found in plain text (possible even in terminal apps, e.g. by using inverted color) to indicate it wasn't found in the original text. Unlike pre-formatting text, this does not lose information.