[dschuessler]

I am unsure how this is supposed to work for CSS. To my knowledge, most CSS properties cannot be substituted for each other. If the subset to be enforced is "CSS properties already present", what is a developer supposed to do if their CSS property is not already present? Change the design?

[QuadmasterXLII]

Well, (like C++) new css attributes are constantly added. This means you constantly have to choose between the old way or the new way: either is fine, but “pick old or new at random on a per pull request basis” isn’t.

[dschuessler]

You seem to assume that old CSS properties can be substituted for new ones. But as I said, to my knowledge this isn’t possible in most cases. Can you give an example of two CSS properties where 'either is fine, but only one should be used'?

Or do you mean something else altogether by 'CSS attributes'?