Consistent way to set CSS for EPUB cover

[gregoriopellegrino]

I think we need a consistent way to set CSS for EPUB cover.

In some reading systems cover images are splitting in multiple virtual pages, e.g.:

[llemeurfr]

I started discussing this with Jiminy Panoz, the author of the Blitz framework.
Notes:

• this is a general issue for images which must be displayed full-page in a reflowable resource.
• resolving that issue in EPUB files for all kinds of reading apps is reaallly cumbersome (see this Blitz issue for a proposed solution).
• a good solution would be IMO to propose a fairly simple best practice which works for most reading apps, especially those supporting EPUB 2 (vs EPUB 2); e.g. based on object-fit. And files issues for the reading apps which don't behave correctly when this best practice is applied.

[gregoriopellegrino]

What about using a declarative solution based on dpub ARIA (https://www.w3.org/TR/dpub-aria-1.0/)?

In this case role="doc-cover"

[clapierre]

I like this approach with using doc-cover and then shouldn't cause issues where an image was meant to cross two page spreads, although not sure if that is one of the use-cases we are trying not to interfere with.

[dauwhe]

I would much prefer that we document best practices rather than asking reading systems to perform special rendering based on markup.

The original images illustrate a massive bug. Images don't fragment, period, no matter what CSS is applied to them.

Some content is not fragmentable, for example many types of replaced elements [CSS2] (such as images or video), scrollable elements, or a single line of text content. Such content is considered monolithic: it contains no possible break points. Any forced breaks within such boxes therefore cannot split the box, and must therefore also be ignored by the box’s own fragmentation context.

[llemeurfr]

Generally speaking, dpub ARIA is about accessibility only; this is not a generic way to add generic semantic tagging to EPUB.
More, a descriptive tagging won't help reading apps which rely on webviews.

[gregoriopellegrino]

Yeah, I realized now that using dpub ARIA wouldn't be really "webby".