Weird text in Vim help files

Question

I found this in my help files. What does it mean? Why is it there?

vim:tw=78:fo=tcq2:isk=!-~,^*,^\|,^\":ts=8:ft=help:norl:

Answer 1

That's a "modeline", a feature of Vim. If it encounters such a line in the first or last 2 lines of a file, Vim reads settings from it and applies them to the current buffer.

Example: Forcing a file with extension .rdf to be handled as file type xml:

<!--
vim: ft=xml
-->
<!-- rest of file -->