Add content scripts section in specification

[oliverdunk]

Adds a first draft of information on content scripts in the specification.

There are still some updates needed, in particular around the algorithm for deciding when to inject a script, but I wanted to open something to get some early feedback.

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Preview | Diff (Both outdated!)

[rdcronin]

Thanks, Oliver! I had a chance to take a quick pass on this one.

[jpmedley]

Sorry for the extra review. I didn't remember that I had looked at this already until I got to my first comment halfway through it.

[Rob--W]

Although not obvious from Github's UI, I just posted additional context on match_about_blank and match_origin_as_fallback:

• match_about_blank: Add content scripts section in specification #542 (comment)
• match_origin_as_fallback: Add content scripts section in specification #542 (comment)

[oliverdunk]

Thanks all! I've just done another pass on this, would appreciate any additional feedback.

[oliverdunk]

@Rob--W, I've addressed all of the actionable feedback here. Could you take another look?

[Rob--W]

I read through it all and considered approving, but then I reached the final section on the algorithm, and since that is inaccurate, I'd like to resolve that before merging.

[Rob--W]

@oliverdunk and I sat together and drafted an updated algorithm that more closely resembles the behavior of Chrome and Firefox. (not Safari because it does not support match_about_blank yet).

We still need to define how to get a precursor origin somehow; ideally that would be in a different spec.

[Rob--W]

Approving to signal that I'm content with the technical accuracy of the document. What remains before merging is formatting so that the spec can render as expected.

Would also be nice to have the "precursor origin" specified somewhere (ideally somewhere not extension-specific because it is a generic concept), but that is not a blocker to merging.

[oliverdunk]

I've updated the formatting following Rob's comment. While CI is passing on this PR, it seems like the preview URL still isn't getting updated. You can find the latest version here: https://github.com/w3c/webextensions/actions/runs/13334183668/artifacts/2594066705

[rdcronin]

LGTM; thank you!

Remaining comments were non-blockers / FYI.