Thread: Kobo Firmware 3.5.0
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Old 07-15-2014, 06:13 PM   #135
Rev. Bob
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Device: Kobo H2O, iPad mini 3, Kindle Touch
Quote:
Originally Posted by PeterT View Post
Unfortunately, no mention of Widows / Orphans @ https://github.com/kobolabs/epub-spec
Sure there is:

Quote:
Originally Posted by The cited page
The ePub 3.0 spec is based on HTML5 and CSS3, adhering to the most recent versions. Content creators are advised to review the HTML5 and CSS3 reference profiles because changes to them could impact file production.
Widows and orphans are defined in CSS, and in this case, the CSS3 specification applies:

Quote:
Originally Posted by The linked document
Normative References

[AltStyleTags] Alternate Style Tags . Elika J. Etemad.

[CSS Namespaces] CSS Namespaces Module . Elika J. Etemad, et al.

[CSS2.0] Cascading Style Sheets, level 2 - CSS2 Specification . Bert Bos, et al. 12 May 1998 (revised 11 April 2008).

[CSS2.1] Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification . Bert Bos, et al. 7 June 2011.
Ah, that's what we want. Since none of the CSS3 modules further down the page address widows/orphans, the CSS2.1 spec applies:

Quote:
Originally Posted by The CSS2.1 spec, section 13.3.2: Breaks inside elements: 'orphans', 'widows'
The 'orphans' property specifies the minimum number of lines in a block container that must be left at the bottom of a page. The 'widows' property specifies the minimum number of lines in a block container that must be left at the top of a page. Examples of how they are used to control page breaks are given below.

Only positive values are allowed.

For information about paragraph formatting, please consult the section on line boxes.
(Boldface mine.) Thus, according to the kobolabs page, the minimum correct value for the widows and orphans properties is one. Not zero, not two (although two is the default value), not -37, but one. Period, full stop, end of debate.

Now, with respect to display bugs, line boxes are also relevant. In its simplest form (but this is VERY simplified; see section 10.8 for the nitty-gritty), the height of a line box is the same as the absolute line-height for the tallest text within that line. Technically speaking, W&O calculations apply to line boxes, so anything that affects those affects W&O display.

Thus, if your font is 20px tall and your line-height is 1.2, the line box is (at least, assuming no weirdness) 24px tall. If the space at the bottom of a page is only 47px, then regardless of how loudly someone argues that there's plenty of room for two lines there, it's just not true. Sure, it's picky - but picky is what computers do. It's their job. When we tell them to be picky about displaying text...well, you know. They'll be ruthlessly picky, in ways that a person applying judgment might not be.
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