Text-first design refers to the practice of designing information so that it is usable/actionable in its most basic plaintext form. It is also a form of progressive enhancement, where the most basic form is text, adding increasing amounts of non-text content such as hyperlinks or images.
Pre-web examples of plain text publishing are a useful source of empirical examples of explicit formatting using only plain text.
Much/most of this was written pre-web (1987-1993), lots of formatting conventions in the examples therein. LOD was constructed by various authors; apparently each author had their own formatting styles. For example:
---------- Test Sets ----------
Test Sets ----------
Test Sets ======
can all mean something we'd now refer to as H2; therefore it offers a wide choice of readable text formatting.
I am including this one not for it's subject matter, but rather as an example of block-quotes and paragraph styling that was common back in the day of 80 column displays and Courier-only printers...
Quotes with attribution:
"Dialectics is the soul of Marxism." [Stalin, _Problems of Leninism_, 1940]
On CNN (11:30 a.m., EDT, Apr.13, 1993), former Stanford Univ. English professor, H. Bruce Franklin, discussed the recent controversy over the Soviet document on U.S. Vietname POWS.