OPF 2 meta tag should not satisfy EPUB 3 metadata requirements #442
Description
EPUB 3 has the OPF2-compatible meta tag that allows name and content attributes on it, but this tag is not meant for expressing metadata in EPUB 3. It's there for a small measure of backwards compatibility with EPUB 2, primarily for being able to identify a cover image.
It came up in w3c/publ-a11y#722 that there are EPUB 3 files expressing the accessibility metadata using this old EPUB 2 meta tag. I was going to reply that Ace should flag these, but after testing I found that it accepts the metadata whichever meta tag you use.
While it's not technically an error to put the accessibility metadata in an OPF2 meta tag for an EPUB 2 reading system, that does not meet the requirements for expressing the information in EPUB 3, so files that only have the info in OPF2 meta tags should fail the metadata requirements.