HTML Tags Reference
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HTML <!DOCTYPE> tag
The HTML !doctype tag is used for specifying which version of HTML the document is using. This is referred to as the document type declaration (DTD).
HTML 4.01 has 3 possible doctypes: HTML 4 Strict, HTML 4 Transitional, and HTML 4 Frameset. Every HTML document you create should have one of these three DTDs.
NOTE: The <!DOCTYPE> tag does not have an end tag!
HTML 4 Strict
This document type includes all HTML elements except those that have been deprecated, and those that appear in frameset documents.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
HTML 4 Transitional
This document type includes all HTML elements including those that have been deprecated.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
HTML 4 Frameset
This document type includes all HTML elements in the transitional DTD as well as those in framed document.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"