Add diff.py to diff individual sections of the source file

[not-my-profile]

Resolves #9694.

[domenic]

I don't think we have anyone willing to maintain this, so it's best kept in the repository of someone who would, such as yourself.

[not-my-profile]

Thanks that makes sense. I'll do that. Would you accept a PR that adds a link to my script to the README? (I guess the "Blame" section could be broadened to "Git tooling").

On a related note do you know if this specific format that's used by the source file in this repository is also used by other specifications? i.e. could my script be of use for other specs as well?

[domenic]

Thanks that makes sense. I'll do that. Would you accept a PR that adds a link to my script to the README? (I guess the "Blame" section could be broadened to "Git tooling").

For sure!

On a related note do you know if this specific format that's used by the source file in this repository is also used by other specifications? i.e. could my script be of use for other specs as well?

Not really, but, maybe for the purposes of your script.

In particular, Wattsi is only used by whatwg/html.

However, the general format of "many sections separated by <hN> elements" is used by a lot of specs.

Some specs use Markdown-like shorthands, as part of the Bikeshed language that they are written in. But most (all?) WHATWG specs use raw <hN> elements instead. For example, https://github.com/whatwg/streams/blob/main/index.bs or https://github.com/whatwg/url/blob/main/url.bs .