Document Type Declaration
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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.
Despite its name, a Document Type Declaration [is not suitable for deducing the type of the document], although apparently it was originally supposed to be.
The HTML layout engines in modern web browsers perform DOCTYPE "sniffing" or "switching", wherein the DOCTYPE in a document served as text/html determines a layout mode, such as "quirks mode" or "standards 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:
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 html.
You can also use a stricter version of HTML if you want. HTML 4.01 does not allow presentational markup with the argument that you should use Cascading Style Sheets for that instead. This is how the strict doctype looks:
See also
- Document Type Definition contains an example
External links
- [Recommended DTDs to use in your Web document] - an informative (not normative) W3C Quality Assurance publication
- [Doctype switch: summary table] - an overview table of the effect of different DOCTYPEs on selecting quirks mode or standards compliance mode in HTML renderers
- [DOCTYPE grid] - another overview table
- [FreeBSD Documentation Project Primer section on DOCTYPE] - has some info about syntax and formal public identifiers
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