Important Advisory to Publishers on EPUB Format: Do not use 'page-map' extension

[Jon]

[I have posted the following to the EPUB Community group...]


I recently became aware that a few publishers are using Adobe's
"page-map attribute extension" in their EPUB publications for mapping
page numbers (such as in a parallel paper book edition) to the EPUB
content.

In principle it is a great feature, and EPUB now provides a standard
way (via NCX) to do this. However, Adobe's proprietary implementation
violates two very clear requirements in the OPF "Package"
specification (OPF is one of the specs which underlie EPUB):

http://www.idpf.org/2007/opf/OPF_2.0_final_spec.html#Section1.4.1.1
(see item iii -- the 'page-map' attribute is not supported in the OPF
Package Schema and thus NOT ALLOWED.)

and

http://www.idpf.org/2007/opf/OPF_2.0_final_spec.html#Section1.4.2
(see item A-iii. A reading system, such as Adobe Digital Editions,
must ignore all Package markup not supported by the OPF Package
schema.)

Therefore, any publisher wishing their EPUB to be fully conformant to
the IDPF specifications MUST NOT use Adobe's 'page-map' extension.

And conforming EPUB reading systems MUST NOT implement the 'page-map'
functionality.

As noted above, the same page mapping functionality is easily enabled
using the NCX <pageList> element, which is supported in EPUB. And I
encourage reading system developers to support it.

Importantly note,too, that all 1.0.x builds of 'epubcheck' prior to
build 1.0.3 had a bug which bypassed Package validation! Thus,
epubcheck did not flag the use of 'page-map' as an error. With this
bug fixed for epubcheck build 1.0.3, publishers will now see that
epubcheck properly flags the use of 'page-map' as an error.

For this and other reasons, publishers should now recheck all their
EPUB publications using epubcheck 1.0.3.

I'll be happy to advise publishers, conversion houses, and reading
system developers on this topic, and on how to implement page mapping
in the NCX document.

(Btw, I also do general consulting on EPUB authoring and full
conformance. Unfortunately 'epubcheck' does not yet implement all the
necessary conformance checks. Thus, at this time it is important that
EPUB publishers have representative EPUB publications checked over by
an EPUB expert for full conformance, as well as recommending best
markup practice.)

Jon Noring
Long-time technical contributor to OPS/OPF/OCF/OEBPS specifications


(p.s., note that I do not speak for the EPUB Working Group, nor for
IDPF, on this matter. I'm only speaking for me, myself and I. However,
the current OPF spec is quite adamant and very clear that Adobe's
extension is NOT ALLOWED. This is a serious issue since one reason for
the two requirements mentioned above -- and I was there during working
group discussions -- is to avoid proprietization of EPUB by some
commercial interest.

I'd also like to make clear that Adobe implemented 'page-map' a long
while back, and they may no longer officially support it after NCX
became a requirement. NCX provides a better, and accessible, solution
to page mapping. So this message is not a knock on Adobe, but rather a
communication to publishers to make sure their EPUB is fully
conformant to the IDPF specifications.

Hopefully, Adobe will publicly drop support for their 'page-map'
extension -- if they haven't already -- and update their "Best
Practices" document to state that NCX should be used for the purpose
of page mapping. And of course I continue to suggest that Adobe's
Digital Editions fully support the NCX <navList> and <pageList> in
addition to <navMap> used for the primary Table of Contents.)