This page needs a saner section ordering. Special (lowercase) properties up front, attributes lexicographic? Importance? Thematic (which used to be the case but not really anymore)?
Topic on Manual talk:Extension.json/Schema
I would consider it appealing to have the same order here as in the schema files. However, we can adjust the order there as well.
I would actually keep the schema files alphabetical (the only reason to interact with them is typically to insert / modify field schemas, and that's easier when they are sorted in an obvious way), and would probably use some kind of thematic / reader-oriented grouping here (and take advantage of the fact that we can add higher-level section headers to make the grouping explicit). I don't think there's any disadvantage of the schema files being in a different order.
We've been talking about using the schema sort order in LibraryUpgrader to enforce the order to something meaningful (keeping attributes together, putting the RL things together, etc.).
The schema file is currently not sorted alphabetically though.
Considering how keeping documentation up to date here usually goes, I think this page will often be outdated in comparison to the actual schema. This is why I prefer using the same ordering here, as it makes it much easier to sync the page with the current schema file.