NationMaster - Encyclopedia: Document Type Declaration

A Document Type Declaration, or DOCTYPE, associates a particular SGML or XML document with a Document Type Definition (DTD). In the serialized form of the document, it manifests as a short string of markup that conforms to a particular syntax. The Standard Generalized Markup Language (SGML) is a metalanguage in which one can define markup languages for documents. ... Jump to: navigation, search The Extensible Markup Language (XML) is a W3C-recommended general-purpose markup language for creating special-purpose markup languages. ... A Document Type Definition (DTD for short) is a set of declarations that conform to a particular markup syntax and that describe a class, or type, of SGML or XML documents, in terms of constraints on the structure of those documents. ... There is more than one usage of the word markup. ...

Despite its name, a Document Type Declaration is not suitable for deducing the type of the document, alhough apparently it was originally supposed to be.

In new browsers for documents served as text/html, the DOCTYPE is used for doctype sniffing in order to choose a layout mode.

Example

A Document Type Declaration can be found in the source code of every Wikipedia page. For example, the first line of many Wikipedia pages reads as follows:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

This Document Type Declaration includes by reference a DTD, whose public identifier is -//W3C//DTD XHTML 1.0 Transitional//EN and whose system identifier is http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd. An entity resolver may you either identifier for locating the referenced external entity. The root element is declared to be html. A public identifier is a document processing construct in SGML. It was subsequently incorporated into XML. In HTML and XML, a public identifier is meant to be universally unique within its application scope. ...

Categories: Software stubs | XML-based standards A Document Type Definition (DTD for short) is a set of declarations that conform to a particular markup syntax and that describe a class, or type, of SGML or XML documents, in terms of constraints on the structure of those documents. ... A Document Type Definition (DTD for short) is a set of declarations that conform to a particular markup syntax and that describe a class, or type, of SGML or XML documents, in terms of constraints on the structure of those documents. ...

Results from FactBites:

HTML Validation: Choosing a DOCTYPE (432 words)
	This declares the document to be XHTML 1.0 Strict.
	This declares the document to be XHTML 1.0 Transitional.
	This declares the document to be XHTML 1.0 Frameset.

Extensible Markup Language (XML) 1.0 (Second Edition) (9190 words)
	The standalone document declaration, which may appear as a component of the XML declaration, signals whether or not there are such declarations which appear external to the document entity or in parameter entities.
	In a standalone document declaration, the value "yes" indicates that there are no external markup declarations which affect the information passed from the XML processor to the application.
	The declaration matches children and the sequence of child elements belongs to the language generated by the regular expression in the content model, with optional white space (characters matching the nonterminal S) between the start-tag and the first child element, between child elements, or between the last child element and the end-tag.

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