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32000-2 Requests: Hamburg

The following items are to be forwarded to the US PDF Reference Committee for consideration during the 2009 Hamburg ISO conference. See PDF/UA's 2008 Beijing Conference requests or 32000-2 Requests: Orlando.

Destination

Request Title 

  Add a "Destination" concept for structure tags.
Request Submitted By   PDF/UA
Executive Summary Make it possible for user to follow a logical reference from one tag to another (such as with an endnote reference and the endnote itself).
Rationale References need to be associated with a note at the logical level to allow AT users navigation to foot- and end-notes while retaining their original place within the document’s logical reading order.
Use Case(s) Any document with footnotes, endnotes, cross-references, sidebars, pull-quotes or other cases in which content refers logically to other content.
Details of Proposed Change

Change to Table 323

Table 323, change ID key from Optional to Required in cases where a Reference tag (See Table 338) is present in the PDF.

New Section

Following 14.8.5.5, add a new section, as follows:

Reference Attribute

If present, the Destination attribute, described in Table (see below) shall appear in a Reference element. It provides viewers following the tag structure with a means to access content (typically footnotes and endnotes) referred to in the text of a document.

Standard Reference Attribute

 Key
 Type
 Value
 Destination  Byte string  (Required) The ID (see Table 323) of the Reference's Destination tag.

Artifacts

Request Title 

 Changes to Table 330
Request Submitted By  PDF/UA
Executive Summary Addresses the need to make artifacts accessible if/when deemed desirable by the author/user.
Rationale Artifacts may or may not have semantic value, even if they do not appear in the tag tree. PDF/UA requires that artifacts be available to AT in principle, if not generally in practice.
Use Case(s)
  • Artifacts are content that may or may not have semantic value; as such, they require that the trappings of semantic value be available (such as alt. text).
  • An AT user wishes to know the document’s as-printed page number, otherwise correctly indicated as an artifact.
Details of Proposed Change

Change to Table 330 – add three new rows:

Key Type Value
Alt Text String (Optional) An alternate description of the artifact in human readable form. 
Lang Text String (Optional) A language identifier specifying the natural language for all text in the artifact. If this entry is absent, the language (if any) specified in the document catalog applies.
ActualText Text String (Optional) Text that is an exact replacement for the artifact. This replacement text (which should apply to as small a piece of content as possible) is useful when extracting the document’s contents in support of accessibility to users with disabilities or for other purposes.
  • The page number referred to above is the "printed" page number, not the ordinal number of the page.
  • PageIdent (see below) appears to be implied by the first explanatory bullet following table 330.  This is misleading and should be modified as follows:

    The following types of artifacts can be specified by the Type entry:

    Pagination artifacts. Ancillary page features such as running heads and folios (page numbers).

  • Table 330, change the Value of the Subtype key to include new valid value:

    PageIdent

Scope and Header attributes of tables

Request Title 

 Modify definition of Scope, Headers, and ID attributes of Tables
Request Submitted By  PDF/UA
Executive Summary Specify an algorithm for associating header cells in a table with data cells in a table.  Additionally, clarify the specification of Scope, Headers, and ID attributes so that header lookup through IDs is well-defined. This modifies the description of these attributes given in Table 337 and Table 349. No new tags or attributes are requested.
Rationale The existing description for tables lacks a precise definition of how headers are associated with table cells.  Such a definition is needed so that authors and AT agree on which header is associated with which cell, especially for non-trivial tables.
Use Case(s) AT needs to know how to find row and column headers associated with each cell.
Details of Proposed Change

The Note to Table 337 says "Lookup is heuristic".  This will lead to inconsistent behavior by AT. No algorithm is given in ISO 32000-1 to address the case in which header cell IDs and table data cell IDs are not present.

In the case that header data cell IDs and table data cell IDs are not specified, this change specifies an algorithm to associate table header cell(s) with table data cell(s). The current ISO 32000 algorithm is flawed. The recursive lookup mentioned in Table 349 (Headers) is ambiguous in that the headers might be only associated with a row, a column, or both. The following suggested change to Table 349 requires that a recursion be explicit.  In particular:

  • HEADER lookup through IDs is not recursive
  • ID order is specified 

The following description of the Headers and Scope attributes should replace the description in ISO 32000, Table 349, Standard table attributes.

 Headers array 

(Optional; not inheritable) An array of byte strings, where each string shall be the element identifier (see the ID entry in Table 323) for a TH structure element that shall be used as a a header associated with this cell.

This attribute may apply to header cells (TH) as well as data cells (TD) (see Table 337). The order in which they are listed shall be row IDs followed by column IDs. The row and column IDs shall be ordered from most specific to most general.

For any cells with an ID listed in Headers, those cells shall specify a Scope so that the header can be determined to be either a row header, a column header or both.
 Scope  name

(Optional; not inheritable) A name whose value shall be with one of the following: Row, Column, or Both. This attribute shall only be used when the structure type if the element is TH (see Table 337).

If a Scope is not specified, then the assumed value for the Scope shall be:

  1. if it is in the first row and column, the scope is assumed to be Both;
  2. otherwise, if it is in the first row, the scope is assumed to be Column.
  3. otherwise, if it is in the first column, the scope is assumed to be Row.
  4. otherwise, the scope is assumed to be Both.
These assumptions are used by the algorithm following Table 337 for determining which headers are associated with a cell.

Below Table 337, delete Note 2 and insert the following text:

If the Headers attribute (Table 349) is not specified, the following algorithm determines which headers are associated with any given cell by finding an ordered list of row and column headers:

To find headers for any data or header cell, search left/up from the cell's position to find row/column header cells. The search in a given direction stops when any of these conditions is reached:

  1. the edge of the table is reached,
  2. a data cell is found after a header cell,
  3. a header cell has the Headers attribute set -- the headers that are specified are appended to the row/column list that is being built.

When a header cell is found in the search and the (implicit or explicit) Scope of the header cell is either Both or Row/Column, the header cell is appended to the end of the list of row/column headers, resulting in a list of headers ordered from most specific to most general.

Informative Note: This algorithm works for languages with different intrinsic directionality of the script (such as right-to-left) because the structure always reflects the reading order of the table.

Line Numbering

Request Title 

 Make line-numbering accessible
Request Submitted By  PDF/UA
Executive Summary Provide sematic structure elements to allow correct tagging of line-numbered content.
Rationale

PDF/UA would require (shall) this structure in the case of line-numbered content, however, new structure elements are required to support the concept.

PDF/UA would then specify usage as follows:

  • The <LineGroup> tag shall enclose content that includes line designators.
  • Line-designator content shall be tagged with a <LineNum> tag.
Use Case(s) Documents that use line-numbered sections.
Details of Proposed Change

Add a new row to Table 333 as follows: 

Structure Type Description
LineGroup A generic block-level element that encloses line-numbered content.

Add a new row to Table 338 as follows:

Structure Type Description

LineNum

 An inline element used for each line number within a LineGroup to tag the line numbers.within a LineGroup block.

Redaction

Request Title 

 Make redaction accessible in PDF
Request Submitted By  PDF/UA
Executive Summary  Ensure that sematic structure elements exist to allow correct tagging of a redacted document.
Rationale While redaction is a common process in government, legal, heathcare and other sectors, no method presently exists for assuring the accessibility of redacted documents.
Use Case(s) See Rationale
Details of Proposed Change

Add new rows to Table 338 as follows:

Structure Type Description
Redaction An inline item (visible or invisible) of content indicating a redaction.
Justification An item of content indicating a justification or explanation (often known as an Exemption Code) for one or more redactions.