If you position yourself as a full stack JavaScript developer and you think talking to 10 lines of non-JS front end code is too much out of a 1 hour long interview I'd be extremely suspicious of how much time you've spent on the front end half of JavaScript integration.
The issue I have with this test is it tells you nothing about the person you are interviewing.
When would you actually create such tags as a fullstack dev? Almost never. 90% of the time, those tags are auto generated by some boiler plate app.
A person that can answer correctly MIGHT be someone that's looked into those tags and done things the hard way, but is that really someone you need to hire? A person that answers incorrectly doesn't necessarily seem like someone I wouldn't hire. After all, what do I care about someone knowing the intricate details of the "html" tag and how it interacts with various browsers? That's write once and forget sort of code.
If you wanted this test to mean anything, why are you picking worthless trivia. Why not, instead, pick something like a function out of jquery or your own code base and ask the same question "Tell me what this function is doing".
"Explain the first ten or so lines of the Twitter source code to me." doesn't read to me like a test, it reads like an opener. Sure, it's possible to show off you know 100% of the trivia for the tags that show up... but more so it's an opener for you to talk to about how much background you know, how much you can relate what you didn't know to things you did or have worked on, and how much you've bothered to go beyond "that boilerplate is generated for me" and look into what the first few lines of the webpages you work on do.
The point does not at all seem to be "Aha, gotcha! You didn't know about the syntax for Apple's limited PWA like functionality offhand in an interview. 5 demerits, next question!".
A person that can hold a good discussion around these tags is both likely to be one that has truly been developing pages for a couple of years and has an interest in learning more than how to make their framework work rather how to make any framework work in a browser. If you're not able to say something cursory about language attributes I'm going to have a hard time believing you've full-stacked a multi-language website (not that I wouldn't but it'd lead to a lot of different questions later). If your response about the doctype line is "it's boilerplate put in by my IDE" my first thought isn't going to be "oh they just spend a lot of time writing code in the rest of the page" it's going to be "they either don't care what the first line of the page is about or it's been so long since they've touch the front end directly they can't say anything about the first tag. I wonder how well they can deal with integrating the front end JS with the page" and steer to towards more about that.
Also the interview was mentioned to be an hour long, if 10 lines of HTML boilerplate, most of which should be on every page, is too far into the weeds of front end time wise then I'd have severe concerns the candidate would be too back-end heavy. Yes, other things should be talked about too, that's why the interview is an hour and this singular question is only about 10 lines.
> 90% of the time, those tags are auto generated by some boiler plate app.
Well, that's a problem. If you don't know how to create a web page with out having to fall back to using "some boiler plate app", I question if you really are a fullstack developer (I would also question if you really can consider yourself a web developer at all, but I know that will just upset people, so I won't go there).
