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Subject: Re: [docbook-apps] FOP and dbfo-need

Hi Peter,
I'm afraid that the dbfo-need processing instruction still does not always work properly in FOP 1.1. It sort of works in some cases, such as between paras or whole lists, but not in other cases.

The PI works by inserting a fo:block-container of the specified height, then backing up using a block with a negative space-before of the same height, and then overwriting the invisible block-container with the text that follows the PI. If the block-container triggers a page break, then it backs up to the top of the next page, as it should. The PI is also supposed to "disappear" space-wise if it does not trigger a page break.

The main problem is that FOP has not fully implemented space-before (see the space-before entry on the FOP standards compliance page, which says "Space adjustment may not fully work everywhere, yet." (http://xmlgraphics.apache.org/fop/compliance.html). As you found, putting the PI between lists works to break the page, but it doesn't adjust the vertical spacing properly if it doesn't break. In the case of the PI inside a variablelist/listitem, FOP outputs the term, breaks the page, and the listitem disappears. In other FO processors like XEP or Antenna House, the term and listitem stay together and bump to the next page as they should.

Because of these problems, the stylesheet by default disables the dbfo-need PI when the stylesheet param 'fop1.extensions' is set to 1. That param should be set when using FOP 1.1. If the PI is having any effect at all, then you must not be setting that param. If that's the case, then you probably aren't getting PDF bookmarks either.

Not all is lost, however. The keep-together processing instruction works in FOP, so you can add it to each varlistentry as follows:

<varlistentry><?dbfo keep-together="always"?>

That will at least prevent each varlistentry from breaking across a page.

Bob Stayton
Sagehill Enterprises

From: "Peter Rosin" <peda@lysator.liu.se>
Sent: Friday, October 04, 2013 9:16 AM
To: <docbook-apps@lists.oasis-open.org>
Subject: [docbook-apps] FOP and dbfo-need


I'm having some trouble with the <?dbfo-need height="2in" ?> processing
instruction. I use DocBook 4.5 with nothing fancy in the stylesheet and
I use FOP-1.1 to generate the PDF.

I have a <variablelist> that spans several pages, some entries are big, some
are small. So, I want to declare how much space some <varlistentry>s need,
in order to make it all not look insanely silly.

The "Soft page breaks" section in chapter 8 of the DocBook XSL guide [1]
hints that I should put the PI inside the <listitem>, but that simply does
not work for me (the content of the <listitem> disappears).

So, I tried to break up the <variablelist> everywhere I need to declare
how much space is needed (by also explicitly specifying the termlength
for each list part, to make them line up). This works, but if the page
break then moves, the broken up <variablelist> inserts a different
amount of space between the last <varlistentriy> of the prior list
and the first entry of the next list. Not very surprising really, but
it is surprising that the vertical space is equal if this PI is not
there. I would have thought that the whole point of this PI was that
it should disappear into thin air if not "invoked" near the end of a

 <!-- some amount of vertical space -->
 <!-- same amount of vertical space -->
<?dbfo-need height="2in" ?>
 <!-- some *other* amount of vertical space, huh? -->

So, while I can make it look good once, it will be a nightmare to
maintain. I basically have to manually page break the document for
every change I make and differently so for every page size I may
decide to render to.

Can anyone offer any advise?


[1] http://www.sagehill.net/docbookxsl/index.html

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