The EPUB 3.3 spec now defines the syntax for the required viewport meta tag for xhtml fixed layout documents: https://w3c.github.io/epub-specs/epub33/core/#app-viewport-meta-syntax
I don't believe epubcheck currently does any checking beyond that the tag is present, though.
The EPUB 3.3 spec now defines the syntax for the required viewport meta tag for xhtml fixed layout documents: https://w3c.github.io/epub-specs/epub33/core/#app-viewport-meta-syntax
I don't believe epubcheck currently does any checking beyond that the tag is present, though.