FO Tree
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The FO Tree is a representation of the XSL:FO document. This represents
the steps Objectify from the spec. The Refinement step is part of reading
and using the properties which may happen immediately or during the layout
process.
Each xml element is represented by a java object. For pagination the
classes are in org.apache.fop.fo.pagination.*, for elements in the flow
they are in org.apache.fop.fo.flow.* and some others are in
org.apache.fop.fo.*.
The base class for all objects in the tree is FONode. The base class for
all FO Objects is FObj.
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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.
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 object will then be given any text data or child elements.
Then the end() 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.
Some validity checking is done during these steps. The user can be warned
of the error and processing can continue if possible.
The purpose of the FO Tree is to hold the information so that it can be
properly processed.
Properties
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The XML attributes on each element are passed to the object. The objects
that represent FO objects then convert the attributes into properties.
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.
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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.
Foreign XML
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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.
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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.
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.
By using element mappings it is possible to read other XML and either
- set information on the area tree
- create pseudo FO Objects that create areas in the area tree
- create FO Objects
Unknown Elements
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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.
Page Masters
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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.
Flow
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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.
Other Elements
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The remaing FO Objects are things like page-sequence, title and
color-profile. These are handled by their parent element.
Associated Tasks
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Create diagrams
Setup all properties and elements for XSL:FO
Setup user agent for property resolution
Verify all XML is handled appropriately
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