Where is the Vim document format specification?

Question

I am trying to find the specification that Vim uses for documentation files (which have a regular .txt extension).

I want to convert some documentation from HTML to a document format that Vim can read and use using the usual syntax : h mydoc , in addition to using the familiar C -] and Co , to jump to any tags in the doc file.

There is a link on the Vim homepage pointing to the specification, but the link is dead, and unfortunately Archive.org does not have a snapshot of the website.

Answer 1

I should have looked more carefully. The help format is described in the help file itself:

:h help-writing 

Answer 2

Another variant:

 :e $VIMRUNTIME/syntax/help.vim 

You will see how the highlighted zones are parameterized.