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							<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE document PUBLIC "-//APACHE//DTD Documentation V1.1//EN"
    "http://cvs.apache.org/viewcvs.cgi/*checkout*/xml-forrest/src/resources/schema/dtd/document-v11.dtd">

<!-- $Id$ -->

<document>
  <header>
    <title>Layout managers</title>
    <authors>
      <person name="Peter B. West" email="pbwest@powerup.com.au"/>
    </authors>
  </header>
  <body>
    <section>
      <title>Layout managers in FOP</title>
      <p>
	What do the layout managers do?  Most layout is is "automatic"
	in the sense of being a straightforward stacking operation.
	Sibling inline-areas, including fo:character areas, are
	stacked in line-areas in the inline-progression-direction.
	Sibling block-areas, including line-areas, are stacked in the
	block-progression-direction.
      </p>
      <p>
	In the simple cases in which both the available
	block-progression-dimension and the available
	inline-progression-dimension are known, this process can be
	driven bottom-up.  Available dimensions trickle down from the
	top, and the bottom level galleys can determine when their
	available areas are full and suspend pending the arrival of
	more areas.  Such full notifications bubble back up the tree
	of active galleys.  E.g., if an inline galley fills a
	line-area of a given inline-p-d and suspends while still
	within the available block-p-d, the parent block-area galley
	will simply stack the inline-area and notify the inline galley
	to continue.  If the inline-galley discovers that the next
	line-area that it would generate will not fit in the the
	block-p-d, it suspends with a notification to that effect to
	its parent.  
      </p>
      <p>
	In more complex cases the dimensions may not be fully
	specified, or decisions about layout may depend on later
	layout.  In all such cases some layout look-ahead is required
	which can report results back to higher layout levels.  The
	job for a layout manager in these cirucmstances is to evaluate
	the information flowing back and set parameters for the best
	fit layout.
      </p>
    </section>
  </body>
</document>