Ebook css informal discussion

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Discussion Summary

This is a brief summary of the discussion topics that were raised during the informal W3C telecon on ebooks and CSS, held at 22 March, 2013. Full minutes of the telecon are available at [1].

Initial note: Bert Bos sent out a document [0] just prior to the call, which the participants did not have enough time to read in order for it to be discussed during the telecon. The chairs suggest an additional telecon to be held to go through this document, as well as follow up on a select set of the topics summarized below.


Luc Audrain noted re pagination how current browser rendering engines (with the exception of Presto) do not implement pagination on screen; EPUB Reading Systems therefore typically implement pagination on top of the browser, which leaves the publisher without the means to assert control/declare intent regarding the pagination behavior. Work within CSSWG (e.g. Presto experiments with extension of the overflow property) on this topic is ongoing.

High Design Layouts (page templates)

Markus Gylling summarized the background of the EPUB Adaptive Layout specification [2] which originated as "Liquid Layout" in Adobe InDesign 6, and subsequently was published as an IDPF informational document. For magazines, textbooks and other publication types where advanced "high design" layouts are used, the kind of feature set that [2] proposes will allow publishers to use adaptive and reflowable styling rather than fixed-layout publications, the latter being suboptimal in many of its current usage contexts. Many publishers within IDPF see this kind of technology as the way of the future. Takeshi Kanai pointed out that optimized display of images is needed to augment high design layouts.

Parts of the EPUB Adaptive Layout specification have been submitted by Adobe to the W3C and is now being worked on within CSSWG (namely CSS Regions, CSS Exclusions and CSS Pagination Templates [4], [5], [6]). Further discussions between CSSWG and IDPF are needed to figure out how the complete desired feature set could be accomplished.

Vertical justification in paginated content

Luc Audrain pointed out that CSS lacks vertical justification. As soon as a certain height is reached in a page, there are problems like widows & orphans, lines, etc.

Selection of equivalent fonts

Luc Audrain noted the problem of font selection when transforming e.g. a PDF into HTML/EPUB, when IPR does not allow to redistribute the original font inside an ebook. What is needed is a mechanism to switch the original font to an "equivalent" one.

Running headers and footers

EPUB defines a custom property for running headers and footers [7], but there are no known implementations at this time. While the urgency for publisher-provided header and footer content seems to vary between publishers/contexts, it is a crucial feature for some to be able to control the appearance and content of these page areas. Further discussions between CSSWG and IDPF are needed to figure out to what extent Paged Media 3 and/or 4 meets the publisher's use cases.

Baseline grids

Alan Stearns mentioned the oft-requested need for a baseline grid in multiple column layouts. This is currently not a priority in CSSWG.

Regions of Interest

Edward O'Connor suggested that the current IDPF work on Regions of Interest (ROI) [8] could be generalized to be used not only for graphic ebooks but also in general on the web.

User control of styling

Brady Duga mentioned that the application of User (and Reading System) styles to content is much more common in ebooks than on the web, cf. features like day-night mode or sepia mode. There is currently no elegant technical way to achieve this in CSS, especially without risking to cause unintended display side effects. Further investigations are needed to understand what needs to be done to better enable User and/or Reading System control of styling (including possibly both CSS and API realms).

i18n: Bopomofo ruby

Murata Makoto pointed out that the current editor-less state of CSS Ruby is problematic, especially as support for bopomofo ruby is important for Taiwanese publishers. A way to ensure that at least parts of CSS Ruby gets back on the REC track is needed.

i18n: missing japanese layout features

Murata Makoto referred to a document produced by the Electronic Book Publishers Association of Japan (EBPAJ) that lists layout features missing for japanese ebook publishers. The call participants requested that W3C and IDPF ask EBPAJ to translate the document to english, so that it can be distributed to a wider audience and help inform future developments. [ed. note: EBPAJ has responded positively to this request, but we dont yet have an ETA for the translation]

Brady Duga mentioned recurring requests from japanese publishers regarding better support for text-level layout, including for example hanging punctuation and line breaking rules. Takeshi Kanai pointed out that each japanese publisher has different line breaking rules, but there are only 4 sets of rules in CSS3 Text. If it was possible to customize line-breaking rules somehow, this would be very helpful to Japanese publishers.

i18n: missing features beyond japanese typography?

Richard Ishida raised the question whether there are prevailing layout-related issues in other locales than Japan that the ebook-industry has been made aware of. Due to telecon time running out, this question was not answered.

[0] http://www.w3.org/Style/2013/paged-media-tasks.html

[1] http://www.w3.org/2013/03/22-ebook-minutes.html

[2] http://idpf.org/epub/pgt/

[3] http://www.ebpaj.jp/images/kumihan.pdf

[4] http://www.w3.org/TR/css3-regions/

[5] http://www.w3.org/TR/css3-exclusions/

[6] http://dev.w3.org/csswg/css-page-template/

[7] http://www.idpf.org/epub/30/spec/epub30-contentdocs.html#sec-css-oeb-head-foot

[8] https://docs.google.com/document/d/1WQ2lX-zVfJKFVimb7AZauDwJnqSzlv_0rbBq1jA8HFA/edit?usp=sharing