Attributes augment the element on which they appear; they also provide additional information about the element.

Attributes appear as name-value pairs in the element's start-tag. For example, to assign the value hostname to the Role attribute of SystemItem, you would use the mark up: <systemitem role="hostname">.


A pointer, verbal or graphical or both, to a component of an illustration or a text object.


"Cooked" data, as distinct from "raw," is a collection of elements and character data that's ready for presentation. The processor is not expected to rearrange, select, or suppress any of the elements, but simply present them as specified.

See Also: Raw.

document type declaration (DTD)

A set of declarations that defines the names of the elements and their attributes, and that specifies rules for their combination or sequence.


Document Style Semantics and Specification Language (ISO/IEC 10179:1996). An international standard stylesheet language for SGML/XML documents.


Elements define the hierarchical structure of a document. Most elements have start and end tags and contain some part of the document content. Empty elements have only a start tag and have no content.


A name assigned (by means of a declaration) to some chunk of data so it can be referred to by that name; the data can be of various kinds (a special character or a chapter or a set of declarations in a DTD, for instance), and the way in which it is referred to depends on the type of data and where it is being referenced: SGML has parameter, general, external, internal, and data entities.


An exclusion is used in a DTD to indicate that, within the element on which the exclusion occurs, the excluded elements are not valid anywhere within the content of the element.

For example, in DocBook, Footnote excludes Footnote. This means that footnotes cannot nest, even though Footnote contains Para, and Footnote occurs in the proper content model of Para.

See Section

external entity

An external entity is a general entity that refers to another document. External entities are often used to incorporate parsable text documents, like legal notices or chapters, into larger units, like chapters or books.

external subset

Element, attribute, and other declarations that compose (part of) a document type definition that are stored in an external entity, and referenced from a document's document type declaration using a public or system identifier.


Text objects like sidebars, figures, tables, and graphics are said to float when their actual place in the document is not fixed. For presentation on a printed page, for instance, a graphic may float to the top of the next page if it is too tall to fit on the page in which it actually falls, in the sequence of words and the sequence of other like objects in a document.

formal public identifier

A public identifier that conforms to the specification of formal public identifers in ISO 8879.


Formatting Output Specification Instance, an SGML document that specifies the appearance or presentation of another SGML document in accordance with the Output Specification DTD defined by MIL-STD-28001C.

general entity

An entity referenced by a name that starts with an ampersand (&) and ends with a semicolon. Most of the time general entities are used in SGML documents, not in the DTD. There are two types, external and internal entities, and they refer either to special characters or to text objects like commonly repeated phrases or names or chapters.


Generic identifier, proper term for the actual name of an element; Para is the generic identifier of the para element.


An inclusion is used in a DTD to indicate that, within the element on which the inclusion occurs, the included elements are valid anywhere within the content of the element.

For example, in DocBook, Chapter includes IndexTerm. This means that IndexTerms can occur anywhere inside chapters, even inside elements that do not have IndexTerms in their proper content models.

See Section

internal entity

A general entity that references a piece of text (including its markup and even other internal entities), usually as a keyboard shortcut.

internal subset

Element, attribute, and other declarations that compose (part of) a document type definition that are stored in a document, within the document type declaration.


Meta-information is information about a document, such as the specification of its author or its date of composition, as opposed to the content of a document itself.

parameter entity

An entity usually referenced in the DTD by a name that starts with a percent sign (%) and ends with a semicolon. In DocBook, parameter entities are mainly used to facilitate customization of the DTD, but they can also be used to control marked sections of a document.

processing instruction

An essentially arbitrary string preceded by a question mark and delimited by angle brackets that is intended to convey information to an application that processes an SGML instance. For example, the processing instruction <?linebreak> might cause the formatter to introduce a line break at the position where the processing instruction occurs.

In XML documents, processing instructions should have the form:

<?pitarget param1="value1" param2="value2"?>

The pitarget should be a name that the processing application will recognize. Additional information in the PI should be added using "attribute syntax."

public identifier

An abstract identifier for an SGML or XML document, DTD, or external entity.


"Raw" data is just a collection of elements, with no additional punctation or information about presentation. To continue the cooking metaphor, raw data is just a set of ingredients. It's up to the processor to select appropriate elements, arrange them for display, and add required presentational information.

See Also: Cooked.


Standard Generalized Markup Language, an international standard (ISO 8879) that specifies the rules for the creation of platform-independent markup languages for electronic texts.


A file that specifies the presentation or appearance of a document; there are several standards for such stylesheets, including CSS, FOSIs, DSSSL, and, most recently, XSL. Vendors often have proprietary stylesheet formats as well.

system identifier

In SGML, a local, system-dependent identifier for a document, DTD, or external entity. Usually a filename on the local system.

In XML, a system identifer is required to be a URI.


An SGML element name enclosed in angle brackets (<>), used to mark up the semantics or structure of a document. <Para> is a tag in DocBook used to mark the beginning of a paragraph.


Uniform Resource Identifier, the W3C's codification of the name and address syntax of present and future objects on the Internet. In its most basic form, a URI consists of a scheme name (such as file, http, ftp, news, mailto, gopher) followed by a colon, followed by a path whose nature is determined by the scheme that precedes it (see RFC 1630).

URI is the umbrella term for URNs, URLs, and all other Uniform Resource Identifiers.


Uniform Resource Locator, a name and address for an existing object accessible over the Internet. is an example of a URL (see RFC 1738).


Uniform Resource Name, the result of an evolving attempt to define a name and address syntax for persistent objects accessible over the Internet; urn:foo:a123,456 is a legal URN consisting of three colon-separated fields: urn followed by a namespace identifier, followed by a namespace specifier (see RFC 1737 and RFC 2141 for details).


The World Wide Web Consortium (


Some elements, such as Chapter, have important semantic significance. Other elements serve no obvious purpose except to contain a number of other elements. For example, BookInfo has no important semantics; it merely serves as a container for the meta-information about a book. Elements that are just containers are sometimes called "wrappers."


The Extensible Markup Language, a subset of SGML designed specifically for use over the Web.


XML Style Language, an evolving language for stylesheets to be attached to XML documents. The stylesheet is itself an XML document.

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