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Said Ryan Ackley
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE document PUBLIC "-//APACHE//DTD Documentation V1.0//EN" "../dtd/document-v10.dtd">
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<document>
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<header>
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<title>HDF</title>
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<subtitle>Word file format</subtitle>
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<authors>
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<person name="S. Ryan Ackley" email="sackley@cfl.rr.com"/>
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</authors>
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</header>
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<body>
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<s1 title="The Word 97 File Format in semi-plain English">
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<p>The purpose of this document is to give a brief high level overview of the
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Word 97 document format. This document does not go into in-depth technical
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detail and is only meant as a supplement to the Microsoft Word 97 Binary
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File Format written by Microsoft.</p>
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<p>The OLE file format is not discussed in this document. It is assumed that
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the reader has a working knowledge of the POIFS API. </p>
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<s2 title="Word file structure">
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<p>A Word file is made up of the document text and data structures
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containing formatting information about the text. Of course, this is a
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very simplified illustration. There are fields and macros and other
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things that have not been considered. At this stage, HDF is mainly
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concerned with formatted text.</p>
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</s2>
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<s2 title="Reading Word files">
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<p>The entry point for HDF's reading of a Word file is the File Information
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Block (FIB). This structure is the entry point for the locations and size
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of a document's text and data structures. The FIB is located at the
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beginning of the main stream.</p>
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<s3 title="Text">
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<p>The document's text is also located in the main stream. Its starting
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location is given as FIB.fcMin and its length is given in bytes by
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FIB.ccpText. These two values are not very useful in getting the text
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because of unicode. There may be unicode text intermingled with ASCII
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text. That brings us to the piece table.</p>
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<p>The piece table is used to divide the text into non-unicode and unicode
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pieces. The size and offset are given in FIB.fcClx and FIB.lcbClx
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respectively. The piece table may contain Property Modifiers (prm).
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These are for complex(fast-saved) files and are skipped. Each text piece
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contains offsets in the main stream that contain text for that piece.
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If the piece uses unicode, the file offset is masked with a certain bit.
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Then you have to unmask the bit and divide by 2 to get the real file
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offset. </p>
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</s3>
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<s3 title="Text Formatting">
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<s4 title="Stylesheet">
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<p>All text formatting is based on styles contained in the StyleSheet.
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The StyleSheet is a data structure containing among other things, style
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descriptions. Each style description can contain a paragraph style and
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a character style or simply a character style. Each style description
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is stored in a compressed version on file. Basically these are deltas
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from another style.</p>
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<p>Eventually, you have to chain back to the nil style which is an
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imaginary style with certain implied values.</p>
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</s4>
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<s4 title="Paragraph and Character styles">
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<p>Paragraph and Character formatting properties for a document's text are
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stored on file as deltas from some base style in the Stylesheet. The
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deltas are used to create a complete uncompressed style in memory.</p>
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<p>Uncompressed paragraph styles are represented by the Pargraph
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Properties(PAP) data structure. Uncompressed character styles are
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represented by the Character Properties(CHP) data structure. The styles
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for the document text are stored in compressed format in the
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corresponding Formatted Disk Pages (FKP). A compressed PAP is referred
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to as a PAPX and a compressed CHP is a CHPX. The FKP locations are
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stored in the bin table. There are seperate bin tables for CHPXs and
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PAPXs. The bin tables' locations and sizes are stored in the FIB.</p>
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<p>A FKP is a 512 byte OLE page. It contains the offsets of the beginning
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and end of each paragraph/character run in the main stream and the
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compressed properties for that interval. The compessed PAPX is based on
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its base style in the StyleSheet. The compressed CHPX is based on the
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enclosing paragraph's base style in the Stylesheet.</p>
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</s4>
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<s4 title="Uncompressing styles and other data structures">
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<p>All compressed properties(CHPX, PAPX, SEPX) contain a grpprl. A grpprl
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is an array of sprms. A sprm defines a delta from some base property.
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There is a table of possible sprms in the Word 97 spec. Each sprm is a
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two byte operand followed by a parameter. The parameter size depends on
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the sprm. Each sprm describes an operation that should be performed on
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the base style. After every sprm in the grpprl is performed on the base
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style you will have the style for the paragraph, character run,
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section, etc.</p>
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</s4>
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</s3>
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</s2>
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</s1>
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</body>
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</document>
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