Reviewing the descriptions: I made this edit as I think fields are supposed to be required, not events.

I'm unsure what the message of this sentence is: "All new schemas for product analytics would include the core identifiers fragment". It could be interpreted as saying that all new schemas should include the core identifiers fragment (because of client_dt being required, as mentioned in this task's description). Or it could be something else.

I find the descriptions that immediately define the scope to be easier to understand and/or work with. pageview_id declares the scope to be "web" immediately. device_id doesn't declare its scope to be apps until the last sentence that mentions that MediaWiki events don't send it. I'll add this as a comment on Gerrit when I have time later, as I'm thinking that whatever's there is the authoritative description and Wikitech only copies it.

Lastly, having this fragment requiring client_dt makes sense to me.

As mentioned, I also left a comment in Gerrit. I see that the descriptions on Wikitech provide more information than the ones in the repository, which makes sense to me. Moving this to the review column.

Thank you for catching that mistake on the wikitech page and fixing it!

I updated the wikitech page and added some clarifications. Please let me know if those are useful and address your concerns.

Yeah, I think the descriptions and clarifications on the wikitech page are great, nice work!

Looks like a sentence in the note in the "Schema fragments" section was cut off: "This fragment provides the client_dt field which." Apart from that I didn't find anything. And again, I think the documentation here is good and really useful!