HTML Tidy the best-known program for auto-formatting HTML markup (i.e.
the HTML source code itself, not the displayed page). It has been used
to format many SRFI documents as well.

The trouble with Tidy is that there are different versions floating
around. Some of them produce subtly different formatting; some don't
support HTML5 which we use for new SRFIs.

The canonical, up-to-date version with HTML5 support seems to be this one:

- https://github.com/htacg/tidy-html5
- http://www.html-tidy.org

Could we standardize on using the latest release of this tool for all
SRFIs? This wouldn't mean that SRFI authors need to use it for every
commit, but that editors and contributors would be free to use it, and
finalized SRFIs would be run through it.

I've found that auto-formatting code/markup saves a lot of time manually
figuring out where line breaks should go and fixing whitespace problems.
In a group effort, it saves debates and back-and-forth edits about which
style is the best (everyone uses whatever style the formatter uses).