EPUB3 fun #2
Aaaaah, forward compatibility... Here are two interesting excerpts from the EPUB Publications 3.0 specification.
In section 3.4.14: Authors may include the
guideelement in the Package Document for EPUB 2 Reading System forwards compatibility purposes
In section 3.4.1: The (
version) attribute (of the
packageelement) must have the value
3.0to indicate compliance with this version of the specification.
Let's look now at two bits coming from the Open Packaging Format (OPF) 2.0.1 specification:
In section 1.4.12: the
versionattribute of the
packageelement is specified with a value of
In section 1.3.2: In addition, to be processed as an OPF 2.0 package, a
versionattribute with a value of
2.0must be specified on the
packageelement. A package element that omits the version attribute must be processed as an OEBPS 1.2 package
<package version="3.0"> is absolutely needed for an EPUB to be parsed as EPUB3 and EPUB2 absolutely requires
<package version="2.0"> since the absence of the
version attribute defaults to OEBPS 1.2!!! Conclusion, "EPUB 2 Reading System forwards compatibility" described in the first quote above is absolutely illusory. Even worse, compatibility can be achieved if and only if EPUB Reading Systems deliberately ignore the
version attribute on the
package element... Ooops, to say the least.