I think a lot of those are bogus, but there are some real ones such as cases where there is no space between attributes, like there are a lot of old elements being used where css could be used instead, probably if the HTML was updated like that and they were smart about selectors it would get the page size down a bit. Then there is the thing which may seem like a lot of bullshit, I don’t know how it now but years ago…
This is still true. Browsers run HN in quirks mode. Just open the devtools console in Firefox, and it will tell you.