A typical DOCTYPE you might see on an HTML document is the HTML 4.01 transitional DOCTYPE. The DOCTYPE isn't exactly an HTML tag or XHTML element. Instead it is a declaration and always appears at the very top of your documents.
A DOCTYPE is made up of the following parts:
- !DOCTYPE
The identifier. It indicates to the user-agent that the enclosed information will define the type of document of the page. - HTML
The Top Element. This tells the browser what element to expect as the top-level element. For HTML and XHTML documents this element would be <html> - PUBLIC
The Availability. The most common DOCTYPES you will use will be publicly available - "PUBLIC". But you can also specify a local DTD with the "SYSTEM" key word. - "-//W3C//DTD HTML 4.01 Transitional//EN"
The Formal Public Identifier. This entire string is what identifies the DOCTYPE.
- -
Registration. If there is a plus-sign (+) here, that means that the organization is registered with the ISO. A minus-sign (-) indicates that it is not registered. - W3C
The Organization. This is the group that owns and maintains the DOCTYPE being used. - DTD
The Type. This defines the type of DOCTYPE used. - HTML 4.01 Transitional
The Human-Readable Label. This is the label that tells you what DTD is being used. It is written so that humans, rather than computers, can understand it. - EN
The Language. This is the language that the DTD is written in. It is not the language of the content of the page.
- "http://www.w3.org/TR/html4/loose.dtd"
The URI. This is an optional URL indicating where the DTD for this DOCTYPE can be found.
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