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							<?xml version="1.0"?>
<document>
  <header> 
   <title>FO Tree</title> 
   <subtitle>All you wanted to know about FO Tree !</subtitle> 
   <authors> <person name="Keiron Liddle" email="keiron@aftexsw.com"/> 
   </authors> 
  </header> 
<body><s1 title="FO Tree">
      <p>
        The FO Tree is a representation of the XSL:FO document. This
        represents the <strong>Objectify</strong> step from the
        spec. The <strong>Refinement</strong> step is part of reading
        and using the properties which may happen immediately or
        during the layout process.
      </p>


<p>Each xml element is represented by a java object. For pagination the
classes are in <code>org.apache.fop.fo.pagination.*</code>, for elements in the flow
they are in <code>org.apache.fop.fo.flow.*</code> and some others are in
<code>org.apache.fop.fo.*.</code></p>


<p>The base class for all objects in the tree is FONode. The base class for
all FO Objects is FObj.</p>


<p>(insert diagram here)</p>


<p>There is a class for each element in the FO set. An object is created for
each element in the FO Tree. This object holds the properties for the FO
Object.</p>


      <p>
        When the object is created it is setup. It is given its
        element name, the FOUserAgent - for resolving properties
        etc. - the logger and the attributes. The methods
        <code>handleAttributes()</code> and
        <code>setuserAgent()</code>, common to <code>FONode</code>,
        are used in this process. The object will then be given any
        text data or child elements.  Then the <code>end()</code>
        method is called.  The end method is used by a number of
        elements to indicate that it can do certain processing since
        all the children have been added.
      </p>


<p>Some validity checking is done during these steps. The user can be warned of the error and processing can continue if possible.
</p>


      <p>
        The FO Tree is simply a heirarchy of java objects that
        represent the fo elements from xml. The traversal is done by
        the layout or structure process only in the flow elements.
      </p>


<s2 title="Properties">


<p>The XML attributes on each element are passed to the object. The objects
that represent FO objects then convert the attributes into properties.
</p>


<p>Since properties can be inherited the PropertyList class handles resolving
properties for a particular element.
All properties are specified in an XML file. Classes are created
automatically during the build process.
</p>


<p>(insert diagram here)</p>


<p>In some cases the element may be moved to have a different parent, for
example markers, or the inheritance could be different, for example
initial property set.</p></s2>


<s2 title="Foreign XML">


<p>The base class for foreign XML is XMLObj. This class handles creating a
DOM Element and the setting of attributes. It also can create a DOM
Document if it is a top level element, class XMLElement.
This class must be extended for the namespace of the XML elements. For
unknown namespaces the class is UnknowXMLObj.</p>


<p>(insert diagram here)</p>


<p>If some special processing is needed then the top level element can extend
the XMLObj. For example the SVGElement makes the special DOM required for
batik and gets the size of the svg.
</p>


<p>Foreign XML will usually be in an fo:instream-foreign-object, the XML will
be passed to the render as a DOM where the render will be able to handle
it. Other XML from an unknwon namespace will be ignored.
</p>


<p>By using element mappings it is possible to read other XML and either</p>
<ul><li>set information on the area tree</li>
<li>create pseudo FO Objects that create areas in the area tree</li>
<li>create FO Objects</li></ul>
</s2>


<s2 title="Unknown Elements">
<p>If an element is in a known namespace but the element is unknown then an
Unknown object is created. This is mainly to provide information to the
user.
This could happen if the fo document contains an element from a different
version or the element is misspelt.</p>
</s2>


<s2 title="Page Masters">
        <p>
          The first elements in a document are the elements for the
          page master setup. This is usually only a small number and
          will be used throughout the document to create new pages.
          These elements are kept as a factory to create the page and
          appropriate regions whenever a new page is requested by the
          layout. The objects in the FO Tree that represent these
          elements are themselves the factory. The root element keeps
          these objects as a factory for the page sequences.
        </p>
</s2>


<s2 title="Flow">
<p>The elements that are in the flow of the document are a set of elements
that is needed for the layout process. Each element is important in the
creation of areas.</p>
</s2>


<s2 title="Other Elements">


        <p>
          The remaining FO Objects are things like page-sequence,
          title and color-profile. These are handled by their parent
          element; i.e. the root looks after the declarations and the
          declarations maintains a list of colour profiles.  The
          page-sequences are direct descendents of root.
        </p>
      </s2>


<s2 title="Associated Tasks">


<ul><li>Create diagrams</li>
<li>Setup all properties and elements for XSL:FO</li>
<li>Setup user agent for property resolution</li>
<li>Verify all XML is handled appropriately</li></ul></s2></s1></body></document>