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9.6 Tagged PDFTagged PDF is a certain kind of enhanced PDF which enables additional features in PDFviewers, such as accessibility support, text reflow, reliable text extraction and conversionto other document formats such as RTF or XML.PDFlib supports Tagged PDF generation. However, Tagged PDF can only be created ifthe client provides information about the document’s internal structure, and obeys certainrules when generating PDF output.Note PDFlib doesn’t support custom structure element types (i.e. only standard structure types as definedby PDF can be used), role maps, and structure element attributes.Cookbook Code samples regarding Tagged PDF issues can be found in the document_interchange categoryof the PDFlib Cookbook.9.6.1 Generating Tagged PDF with PDFlibCookbook A full code sample can be found in the Cookbook topic document_interchange/starter_tagged.Required operations. Table 9.18 lists all operations required to generate Tagged PDFoutput. Not calling one of the required functions while in Tagged PDF mode will triggeran exception.Table 9.18 Operations which must be applied for generating Tagged PDFitemTagged PDF outputdocument languagestructureinformationPDFlib function and option requirements for Tagged PDF compatibilityThe tagged option in PDF_begin_document( ) must be set to true.The lang option in PDF_begin_document( ) should be set to specify the natural language of thedocument. It should initially be set for the document as a whole, but can later be overridden forindividual items on an arbitrary structure level.Structure information and artifacts must be identified as such. All content-generating API functionsshould be enclosed by PDF_begin_item( ) / PDF_end_item( ) pairs.Unicode-compatible text output. When generating Tagged PDF, all text output mustuse fonts which are Unicode-compatible as detailed in Section 5.4.4, »Unicode-compatibleFonts«, page 111. This means that all used fonts must provide a mapping to Unicode.Non Unicode-compatible fonts are only allowed if alternate text is provided for the contentvia the ActualText or Alt options in PDF_begin_item( ). PDFlib will throw an exceptionif text without proper Unicode mapping is used while generating Tagged PDF.Note In some cases PDFlib will not be able to detect problems with wrongly encoded fonts, for examplesymbol fonts encoded as text fonts. Also, due to historical problems PostScript fonts withcertain typographical variations (e.g., expert fonts) are likely to result in inaccessible output.Page content ordering. The ordering of text, graphics, and image operators which definethe contents of the page is referred to as the content stream ordering; the contentordering defined by the logical structure tree is referred to as logical ordering. TaggedPDF generation requires that the client obeys certain rules regarding content ordering.The natural and recommended method is to sequentially generate all constituentparts of a structure element, and then move on to the next element. In technical terms,the structure tree should be created during a single depth-first traversal.216 Chapter 9: Generating various PDF Flavors
A different method which should be avoided is to output parts of the first element,switch to parts of the next element, return to the first, etc. In this method the structuretree is created in multiple traversals, where each traversal generates only parts of an element.Importing Pages with PDI. Pages from Tagged PDF documents or other PDF documentscontaining structure information cannot be imported in Tagged PDF mode sincethe imported document structure would interfere with the generated structure.Pages from unstructured documents can be imported, however. Note that they willbe treated »as is« by Acrobat’s accessibility features unless they are tagged with appropriateActualText.Artifacts. Graphic or text objects which are not part of the author’s original contentare called artifacts. Artifacts should be identified as such using the Artifact pseudo tag,and classified according to one of the following categories:> Pagination: features such as running heads and page numbers> Layout: typographic or design elements such as rules and table shadings> Page: production aids, such as trim marks and color bars.Although artifact identification is not strictly required, it is strongly recommended toaid text reflow and accessibility.Inline items. PDF defines block-level structure elements (BLSE) and inline-level structureelements (ILSE) (see the PDFlib Reference for a precise definition). BLSEs may containother BLSEs or actual content, while ILSEs always directly contain content. In addition,PDFlib makes the following distinction:Table 9.19 Regular and inline itemsaffected itemsregular itemsall grouping elements andBLSEsinline itemsall ILSEs and non-structuraltags (pseudo tags)regular/inline status can be changed no only for ASpan itemspart of the document’s structure tree yes nocan cross page boundaries yes nocan be interrupted by other items yes nocan be suspended and activated yes nocan be nested to an arbitrary depth yes only with other inline itemsThe regular vs. inline decision for ASpan items is under client control via the inline optionof PDF_begin_item( ). Forcing an accessibility span to be regular (inline=false) is recommended,for example, when a paragraph which is split across several pages containsmultiple languages. Alternatively, the item could be closed, and a new item started onthe next page. Inline items must be closed on the page where they have been opened.Recommended operations. Table 9.20 lists all operations which are optional, but recommendedwhen generating Tagged PDF output. These features are not strictly re-9.6 Tagged PDF 217
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PDFlib GmbH München, Germanywww.pd
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Contents0 Applying the PDFlib Licen
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5.6.1 Standard CJK Fonts 1165.6.2 C
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10.2.2 Block Properties 22710.2.3 W
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0 Applying the PDFlib License KeyAl
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Licensing options. Different licens
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PDFlib TET (Text Extraction Toolkit
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PDFlib can be integrated directly i
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Improved handling of Chinese, Japan
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1.4 Features in PDFlib/PDFlib+PDI/P
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1.5 Availability of Features in dif
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24 Chapter 1: Introduction
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2.2 COM Binding(This section is onl
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necessary. After fatal exceptions t
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2.4 C++ BindingIn addition to the p
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PDFlib servlets and Java applicatio
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2.6 .NET Binding(This section is on
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More than one way of String handlin
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PHP on Windows will find files with
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2.10 REALbasic Binding 1(This secti
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Now you can compile your program us
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2.13 Tcl BindingInstalling the PDFl
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Error policies. When PDFlib detects
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plied), but only the corresponding
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name exactly as supplied and try to
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3.1.4 Generating PDF Documents in M
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3.2 Page Descriptions3.2.1 Coordina
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In order to facilitate the use of t
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Merely constructing a path doesn’
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3.3 Working with ColorNote The PDFl
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where is the identifier of the col
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Rendering Intents. Although PDFlib
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p.set_parameter("errorpolicy", "ret
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with a thin black border. Initially
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}p.begin_page_ext(pagewidth, pagehe
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Table 3.5 Parameters for the JavaSc
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4.2 Important Unicode ConceptsChara
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4.3 Strings in PDFlib4.3.1 String T
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EBCDIC UTF-8 BOM). If the usehypert
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values 0x7B and 0x7D must be preced
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Table 4.4 Availability of glyphs fo
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exclam 33 0x0021...If no Unicode va
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Table 4.5 Predefined CMaps for Japa
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4.6 Addressing Characters and Glyph
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Table 4.8 Control characters and th
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glyphcheck=replace: silent approach
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94 Chapter 4: Unicode and Legacy En
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5.1.2 Font EncodingsAll fonts for t
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5.2 Font Format Details5.2.1 PostSc
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the contents of the characters in a
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Path resource category (again, the
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When working with host fonts it is
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Note The Leopard builds of PDFlib (
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put by default. For encodings which
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5.4.2 Glyph ID Addressing for TrueT
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5.5 Font Metrics and Text Variation
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Temporarily disabling kerning may b
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5.6 Chinese, Japanese, and Korean F
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CJK host font names on Windows can
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120 Chapter 5: Font Handling
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tion) if the user coordinate system
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color: black and white, grayscale,
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PDFlib supports three kinds of tran
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BMP> PNG> JPEG> TIFF> GIFFor images
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6.2 Importing PDF Pages with PDI (P
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Alternatively, you can use the pdiu
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20Kraxitext on top right of the box
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can be used. In Figure 7.5h the tex
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7.1.5 Placing a StampCookbook A ful
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7.2 Multi-Line TextflowsIn addition
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piece of normal text. Font, font si
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leftindent = 15parindent = 20leadin
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hortabmethod rulertabalignment left
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leftindent = &indentparindent = - &
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To fold the famous rocket looper pr
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Our paper planes are the ideal way
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Our paper planesare the ideal way o
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p.fit_textflow(textflow, left_x, le
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7.3 Placing Images and Imported PDF
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Fig. 7.28 Fitting an image into a b
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Fitting an oriented image into a bo
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7.4 Table FormattingThe table forma
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Page 174 and 175: The table in Figure 7.42 is spread
Page 176 and 177: Splitting a row. If the last body d
Page 178 and 179: To increase the box height to match
Page 180 and 181: Fig. 7.48 Using the image matchbox
Page 182 and 183: size of a page. Determining the pag
Page 184 and 185: 8.3 Composite Data Structures and I
Page 186 and 187: Table 8.2 pCOS path prefixesprefixl
Page 188 and 189: Table 8.3 Universal pseudo objectso
Page 190 and 191: Table 8.4 Pseudo objects for PDF ob
Page 192 and 193: Table 8.5 Pseudo objects for resour
Page 194 and 195: 194 Chapter 8: The pCOS Interface
Page 196 and 197: Table 9.2 PDFlib features for PDF 1
Page 198 and 199: to disable any access restrictions.
Page 200 and 201: Table 9.4 Access restriction keywor
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Page 204 and 205: Table 9.6 Operations which must be
Page 206 and 207: work as a full PDF/X validator or t
Page 208 and 209: 9.5.2 Generating PDF/A-conforming O
Page 210 and 211: Table 9.11 Additional requirements
Page 212 and 213: This statement will retrieve a stri
Page 214 and 215: Table 9.16 Predefined XMP schemas f
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Page 220 and 221: * 1 create top part of left column
Page 222 and 223: optlist = "Title=Insert parent=" +
Page 224 and 225: exported to other formats. If the A
Page 226 and 227: Click Add... and select the PDFlib
Page 228 and 229: scaling factor or rotation. For eac
Page 230 and 231: 10.3 Using the PDFlib Block Plugin
Page 232 and 233: next step other objects which are p
Page 234 and 235: Use Ctrl-V (on Windows) or Cmd-V (o
Page 236 and 237: Associating form fields with corres
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Page 240 and 241: 10.5 Standard Properties for Automa
Page 242 and 243: 10.5.2 Text PropertiesText-related
Page 244 and 245: Table 10.6 Textflow block propertie
Page 246 and 247: Table 10.6 Textflow block propertie
Page 248 and 249: 10.6 Querying Block Names and Prope
Page 250 and 251: 10.7 PDFlib Block SpecificationThe
Page 252 and 253: Example. The following fragment sho
Page 254 and 255: 254 Chapter 10: Variable Data and B
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Page 258 and 259: Ffeatures of PDFlib 20fill 57font m
Page 260: TrimBox 57TrueType fonts 95TTC (Tru
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