DTD Options

HTML 4.01 and XHTML 1.0 offer three DTD versions:

  • Strict

  • Transitional

  • Frameset

XHTML 1.1 has only one DTD. The DTD documents live on the W3C server at a stable URL.

The <!DOCTYPE> (document type) declaration contains two methods for pointing to DTD information: one is a publicly recognized document identifier; the other is a specific URL in case the browsing device does not recognize the public identifier. Descriptions and specific markup for each HTML and XHTML version are listed here.

HTML 4.01 Strict

The Strict DTD omits all deprecated elements and attributes. If you are authoring according to the strict DTD, use this document type definition:

    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
     "http://www.w3.org/TR/HTML4.01/strict.dtd">
HTML 4.01 Transitional

The Transitional DTD includes everything from the Strict DTD, plus all deprecated elements and attributes. If your document includes some deprecated elements or attributes, point to the Transitional DTD using this DOCTYPE declaration:

    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
     "http://www.w3.org/TR/HTML4.01/loose.dtd">
HTML 4.01 Frameset

If your document contains frames—that is, it uses frameset instead of body for its content—then identify the Frameset DTD. The Frameset DTD is the same as the Transitional version (it includes deprecated yet supported elements and attributes), with the addition of frame-specific elements. The content-containing HTML documents that are displayed within the frames ...

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