EPUB3 fun #9
meta elements in EPUB3 triggers a few surprises... In fact, that's not the
meta elements themselves, it's the properties they carry. Let me explain:
metaelements carry a
- a property is a keyword optionally preceded by a property vocabulary prefix and a colon
- EPUB3 Media Overlays use the reserved
mediaprefix mapped to namespace
- the Media Overlays says the
media:durationproperty has a cardinality of "exactly one for the Publication and for each Media Overlay"
In fact, that's quite painful and costly to test in the following case:
- suppose the namespace above is declared (yes, I know it's already reserved but it's not forbidden to do it !!!) on the
prefixattribute with prefix
- suppose we have one
<meta property="media:duration">in the OPF for the Publication
- but also a
<meta property="foo:duration">for the same value...
- that's invalid per spec, see the last item of the list above
You can't compare the prefixes, that's not enough. You really need to rely on URIs and that's where validation is expensive.
Conclusion: Media Overlays 3.0 have been released with EPUB3. The associated
media prefix should be dropped and its related properties should be prefixless in EPUB3. If the issue is the
media:narrator property too close to a value in another property vocabulary, it should be changed.