PDF Techniques
for Web Content Accessibility Guidelines 1.0 and 2.0

PDF Glossary

40 bit encryption

@@

128 bit encryption

@@

Accessibility permission

A PDF file can be encrypted (PDF 1.1) to protect its contents from unauthorized access. PDF's standard security handler defines a set of access privileges for a document, including privileges such as modifying the document's contents, copying text and graphics from the document, and printing the document. In PDF 1.4, this set includes accessibility permission, which controls whether the contents of the document are available via standard accessibility APIs to screen readers and other assistive technology.

ActualText value

Sometimes characters are rendered by graphics commands other than showstring. For instance, an illuminated character may be rendered by an image or a series of graphics commands. In this situations, the Actual Text property is used to identify the character being rendered. This character may be concantentated with adjoining text to form a word.

Adobe glyph name

The name of a character in the Adobe standard character encodings, in Appendix D of the PDF 1.3 Reference Manual. The encodings list characters, character names, and character codes used in platform standard encodings.

Article flows

@@

Artifacts

A page element that is a side effect of rendering, rather than an intrinsic part of the document or story. For example, artifacts of the printing process might include crop-box markings or the document file name printed outside the crop box. Artifacts of the pagination of a document are elements that would be absent (or present in a different form) if the document was always one very big page. So pagination artifacts include running headers and page. A horizontal rule above a foornate would be an artifact of the layout process and typographic style.

Assistive Technology Devices

@@

Authoring Tools

@@

Bookmarks

@@

Characters

A character is a printable symbol having phonetic or pictographic meaning and usually forming part of a word of text, depicting a numeral, or expressing grammatical punctuation. A character is generally one of a limited number of symbols, including the letters of a particular language's alphabet, the numerals in the decimal number system, and certain special symbols such as the ampersan

Character codes

A show string is the encoded representation of a sequence of non-negative integers. Each of those integers is a Character Code. The interpretation of a show string depends on the associated font: some fonts imply a one-byte representation while others imply a multi-byte representation. Note: This is the PDF definition of character code and somewhat con-trary to normal usage. The same letter, for example a capital A, can have many different character codes on the same page.

Character Encoding

Character encoding is a table in a font or a computer operating system that maps character codes to glyphs in a font. Most operating systems today represent character codes with an 8-bit unit of data known as a byte. Thus, character encoding tables today are restricted to at most 256 character codes.

Not all operating system manufacturers use the same character encoding. For example, the Macintosh platform uses the standard Macintosh character set as defined by Apple Computer, Inc., while the Windows operating system uses another encoding entirely, as defined by Microsoft. Fortunately, standard Type 1 fonts contain all the glyphs needed for both these encodings, so they work correctly not only with these two systems, but others as well.

Column headers

@@

CMap

A CMap specifies the mapping from character codes to character selectors (CIDs, character names, or character codes) in one or more associated fonts or CIDFonts. It serves a function analogous to the Encoding dictionary for a simple font. A Cmap also specifies the writing mode - horizontal or vertical - for any CIDFont with which the CMap is combined.
Also a CMap (character map) file specifies the correspondence between character codes and the CID (character identifier) numbers used to identify characters. For composite (Type 0) fonts, it is the equivalent to the concept of an encoding in a simple font. A CMap can describe a mapping from multiple-byte codes to thousands of characters in a large CID-keyed font.

Concatenate

To combine character strings, to join together two or more files or lists to form one big one. Example: The Unix cat command can be used to concatenate files.

Content extraction

@@

Contrast

A subjective feeling that graphic elements (such as fonts) are different but work together well. This gives a feeling of variety without losing harmony. Within a particular font, contrast also refers to the variety of stroke thicknesses that make up the characters. Helvetica has low contrast and Bodoni has high contrast.

Crop box

The crop box defines the region to which the contents of the page are to be clipped (cropped) when displayed or printed.

Crop box markings

@@

Cross page environment

@@

Data tables

@@

Encoding

Mapping from a character set definition to the actual code units used to represent the data. See also character encoding

Expansion

@@

Form fields

@@

Glyph

An image used in the visual representation of characters; roughly speaking, how a character looks. A font is a set of glyphs. In the simple case, for a given font (typeface and size), each character corresponds to a single glyph but this is not always the case, especially in a language with a large alphabet where one character may correspond to several glyphs or several characters to one glyph (a character encoding). A glyph can be an alphabetic or numeric font or some other symbol that pictures an encoded character. The following quote is from a document written as background for the Unicode character set standard. An ideal characterization of characters and glyphs and their relationship may be stated as follows: A character conveys distinctions in meaning or sounds. A character has no intrinsic appearance. A glyph conveys distinctions in form. A glyph has no intrinsic meaning. One or more characters may be depicted by one or more glyph representations (instances of an abstract glyph) in a possibly context dependent fashion. Glyph is from a Greek word for "carving."

Indexing value

@@

Line-break hyphen or Hard hyphen

Hyphens that you add explicitly by entering the dash character are called line-break or hard hyphens. A hyphen that is always set; for example, the hyphen in "cost-effective." A soft hyphen, by contrast, will only be set when a word that is not normally hyphenated falls at the end of a line, and must be broken for proper type spacing. Word processors use two basic techniques to perform hyphenation. The first employs an internal dictionary of words that indicates where hyphens may be inserted. The second uses a set of logical formulas to make hyphenation decisions. The dictionary method is more accurate but is usually slower. The most sophisticated programs use a combination of both methods. Most word processors allow you to override their own hyphenation rules and define yourself where a word should be divided.

Link text

@@

Logical structure tree

A PDF facility that allows the structure of a PDF file to be expressed via a Logical Structure. Ref: PDF Reference, section 8.4.3. The Logical Structure is separable from Tagged PDF, although Tagged PDF requires the use of Logical Structure. Every Tagged PDF is a Logical Structured PDF, but not all Logical Structured PDF files are Tagged PDFs.

MacRomanEncoding, MacExpertEncoding, or WinAnsi Encoding

The regular font encodings used for Latin-text fonts on mac OS and Windows systems are named MacRomanEncoding and WinAnsiEncoding, respectively. Additionally, an encoding named MacExpertEncoding is used with "expert" fonts that contain addiitonal characters useful for sophisticated typography. Complete details of these encodings and the characters present in typical fonts are found in Appendix D of the PDF Version 1.3 Reference Manual.

Map, mapped

@@.

Markup

@@

Non-proprietary

@@

The rendered text content of a link.

Objects

An object is an identifiable, encapsulated entity that provides one or more services requested by a client. Objects can refer to the objects in OOP (object-oriented programming) or the objects in OLE (Object Linking and Embedding). In object-oriented programming, objects are the things you think about first in designing a program and they are also the units of code that are eventually derived from the process. In between, each object is made into a generic class of object and even more generic classes are defined so that objects can share models and reuse the class definitions in their code. Each object is an instance of a particular class or subclass with the class's own method or procedures and data variable. An object is what actually runs in the computer. An object can be a spell checker or a piece of a graphics program used to draw squares or circles. Do you remember the crazy story people used to try to tell about a word processer where you could pick all of your favorite pieces (favorite spell checker, grammar checker, text editor, font manager, etc.) and piece them together to form the ultimate customizable word processer? Well, those pieces are objects. In OLE, an object is a piece of a document, a graphic, or some multimedia. In general multimedia terms, an object is a stored data element, such as a video clip, an audio file, or a graphic representation of an object.

Output Format

@@

Output method

@@

Page-content stream

A page's content stream contains operands and operators used to place "paint" on a page in selected areas. By executing the actions described in the page content stream, an application builds up the image of the page described by the stream.

Page oriented

@@

Pagination

@@

Protocols

A formal description of message formats and the rules two computers must follow to exchange those messages. Protocols can describe low-level details of machine-to-machine interfaces (e.g., the order in which bits and bytes are sent across a wire) or high-level exchanges between allocation programs (e.g., the way in which two programs transfer a file across the Internet).

Reading order

@@

Reflow

@@

ReverseChars

Font characteristics may suggest that right-to-left text be typeset left-to-right. The ReverseChars marked content indicates that the show strings within the marked content are individually reversed in reading order.

Running headers

@@.

Showstring

(a la Loretta) The strings that are the arguments to the PDF and Postscript text-showing operators that show text on a page. The show string is interpreted as a sequence of character codes identifying the glyphs to be painted.

Showstring operations

@@.

Spacing characters

@@.

Soft hyphen

(a la Loretta) A character that is used to mark conditional hyphenation points. Unicode and ISO_Latin-1 code-point 0xAD.
A hyphen that will only be set if the word falls at the end of a line which is too long, and has to be broken. Hyphens inserted automatically by a hyphenation utility are called discretionary or soft hyphens. Word processors use two basic techniques to perform hyphenation. The first employs an internal dictionary of words that indicates where hyphens may be inserted. The second uses a set of logical formulas to make hyphenation decisions. The dictionary method is more accurate but is usually slower. The most sophisticated programs use a combination of both methods. Most word processors allow you to override their own hyphenation rules and define yourself where a word should be divided.

Tagged PDF

Is a version od PDF that provides structure and orders information to allow PDF documents to be read by screen-readers and to be reflowed to fit different display screen sizes. To accomplish this, Tagged PDF marks, or tags, the various elements that make up a page.

Tagging

The association of attributes of text with a point or range of the primary text. The value of a particular tag is not generally considered to be a part of the "content" of the text. A typical example of tagging is to mark the language or the font for a portion of text.

Trailing space character

A white space character inserted into the text for a page after the last word on a line. A trailing space character is not needed to produce the correct page image, but is important for determining word breaks in the text of the page.

Type 0 font, Type 1 font

Type 0 font: a composite font, that is, a font composed of other fonts, organized hierarchically.
Type 1 font: a font represented using the Adobe Type 1 Font Format. A Type 1 font program is a stylized PostScript program that describes glyph shapes.

Typographic style

@@.

Unicode

A character coding scheme that uses 16 bits for each character, designed to extend the capabilities of ASCII, which uses seven bits. Nearly all letters and symbols in all languages can be represented in a standard way with Unicode. The first 128 characters of Unicode are identical to those in standard ASCII. Unicode is an entirely new idea in setting up binary codes for text or script characters. Officially called the Unicode Worldwide Character Standard, it is a system for "the interchange, processing, and display of the written texts of the diverse languages of the modern world." It also supports many classical and historical texts in a number of languages. Currently, the Unicode standard contains 57709 distinct coded characters derived from 24 supported language scripts. These characters cover the principal written languages of the world. Originally Unicode was designed to be universal, unique, and uniform, i.e., the code was to cover all major modern written languages (universal), each character was to have exactly one encoding (unique), and each character was to be represented by a fixed width in bits (uniform). Parallel to the development of Unicode an ISO/IEC standard was being worked on that put a large emphasis on being compatible with existing character codes such as ASCII or ISO Latin 1. To avoid having two competing 16-bit standards, in 1992 the two teams compromised to define a common character code standard, known both as Unicode and BMP. Since the merger the character codes are the same but the two standards are not identical. The ISO/IEC standard covers only coding while Unicode includes additional specifications that help implementation. Unicode is not a glyph encoding. The same character can be displayed as a variety of glyphs, depending not only on the font and style, but also on the adjacent characters. A sequence of characters can be displayed as a single glyph or a character can be displayed as a sequence of glyphs. Which will be the case, is often font dependent.

Unicode value

(a la Loretta)Unicode value or code point: The Unicode Consortium defined a set of sixteen-bit code points, 57709 of which are currently assigned and named Unicode Characters. The lowest 65536 code-points in ISO 10646-1 1993 are idential to the Unicode Standard and are sometimes called the Basic Multilingual Plane. See http://www.unicode.org

Unicode character

@@

User agents

Software to access Web content, including desktop graphical browsers, text browsers, voice browsers, mobile phones, multimedia players, plug-ins, and some software assistive technologies used in conjunction with browsers such as screen readers, screen magnifiers, and voice recognition software.

User name (/TU key)

Any interactive form field may contain the optional /TU entry in its dictionary. This entry, known as the user name or short description, is used to identify this field when generating an error message or naming the field to a screen reader.

Word breaks

Applications divide the text of a page into words; word breaks are the points in the text stream that separate adjoining words. Different applications may use different rules for defining words; for example, one application may consider everything between white space characters to be a word. Another application may not include leading or trailing punctuation as part of a word.

PDF References