mdtoc/docs/john_gruber.md

John Gruber is the creator of Markdown.
He describes the syntax here:
https://daringfireball.net/projects/markdown/syntax

headers

https://daringfireball.net/projects/markdown/syntax#header

Atx-style headers use 1-6 hash characters at the start
of the line, corresponding to header levels 1-6.

=> that means header level 6 is the maximum level (vim and bat also do not highlight
level 7 headings)

But there are also "Setext-style headers" that can only create
level 1 and 2 headers.

Any number of underlining =’s or -’s will work.

bat does not detect "setext" at all.
vim interprets a line that is followed by a line with at least one
= or - as a header. (that line may not include any other characters than
- or = and they may not be mixed)