I read somewhere recently that the “meta tags for search engine placement” concept is less important than it used to be, as the main search engines use their own techniques, bypassing the potential abuse meta tags can be (and frequently were) subject to.
Meta tags can still have other roles to play in a web page, but I think search engines aren’t really the primary one anymore.
It’s been a while so while I don’t remember the details I remember placing a bare list (UL or OL) gives an error and I remember there was a way around that which I do not quite remember now but it produced some problem which the invalid code did not so I would just leave the bare lists rather than enclose them in whatever tags make them valid code.
Another one is that HR does not legally admit the color as in
I have found the following to be valid
but most of the times the invalid code worked fine, if not better, and is simpler.