Setext (.stx) was a standard for ASCII text that allowed for some simple text formatting, that dates from the late 80s. It was used for email newsletters like TidBits, and there were a variety of viewers that could display it.
It is very similar to TextFormattingRules, but has some differences, in particular in the area of headers.
- Overview http://docutils.sourceforge.net/mirror/setext/setext_concepts_Aug92.etx.txt
- Commentary http://docutils.sourceforge.net/mirror/setext.html
It has been superseded by StructuredText and ReStructuredText.