Add index() function to CSS package

[tidoust]

The function creates an indexed structure more aligned with MDN data. The README documentation was also updated to detail remaining structural nuances, and more importantly differences in content between the two projects.

[tidoust]

The CI test failure is unrelated, but I still need to understand why it gets raised. As far as I can tell, the problematic type was introduced in main after that pull request got created and tests should not run against data in main.

I do see a minor flaw in the code that applies "freeze" patches (the code assumes that it needs to return to main afterwards). But that should not have much consequences on top of leaving the client on the wrong branch afterwards.

[tidoust]

The CI test failure is unrelated, but I still need to understand why it gets raised. As far as I can tell, the problematic type was introduced in main after that pull request got created and tests should not run against data in main.

And now I understand. For some reason, I assumed that the checkout action in a pull request checked out the data at the latest PR commit. It actually performs a merge with the main branch, which explains why the (unrelated) error appears.

I do see a minor flaw in the code that applies "freeze" patches (the code assumes that it needs to return to main afterwards). But that should not have much consequences on top of leaving the client on the wrong branch afterwards.

That flaw does exist, and indeed does not have much consequences. I'll fix it in another PR.