“For example, a large screen view with a mega menu, more content, and more complicated interface would not be a conforming alternative to a view optimized for small screen because the two have different functionality.”
I think we need a clearer example (or to drop the example).
· Mega menus can easily be better than a mobile equivalent. For example, sites that have a mega menu for wide-screens often create a hamburger menu for small screens, then forget to properly hide the options at mobile size.
· If the small screen version is missing content isn’t that is also a problem? I think that case is covered in note 2.
· We’d need to define complex interface, good luck! ;-)
How about taking a different tack:
“Sometimes specifically optimized views are delivered to the user agent based on screen size, device type, etc. A WCAG conforming view linked from such an optimized view could only be considered a conforming alternative if it has equivalent content and functionality as the optimized view. The website should not assume users have access to alternative devices.”
Jon: The term mega-menu implies that there is a menu with very large drop-downs, usually with at least a dozen options per drop-down in multiple columns. Visually the drop-downs often cover most of the page, so they are not very mobile friendly without being made responsive.
A (good) example of a mega-menu:
https://adobe-accessibility.github.io/Accessible-Mega-Menu/
Cheers,
-Alastair