html5 has only one doctype declaration, the syntax ""; and the "" declaration must be located in the first line of the HTML5 document, that is, in " ” tag, it tells the browser that the document uses the HTML specification.
The operating environment of this tutorial: Windows 7 system, HTML5 version, Dell G3 computer.
doctype declaration in html5
There are three declarations in HTML 4.01, but there is only one in HTML 5, And it's very simple: the
<!DOCTYPE HTML>
declaration must be on the first line in the HTML5 document, before the <code> tag. This tag tells the browser the HTML specification used by the document.
The doctype declaration is not an HTML tag, it is an instruction that tells the browser the version of markup used to write the page.
It is very important to specify the doctype in all HTML documents so that the browser understands the expected document type.
The tag has no closing tag and is not case-sensitive.
Extended knowledge: doctype declarations in HTML 4.01
HTML 4.01 Strict
The DTD Contains all HTML elements and attributes, except presentational and deprecated elements (such as font). Framesets are not allowed.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
HTML 4.01 Transitional
This DTD contains all HTML elements and attributes, including presentational and deprecated elements (such as font) . Framesets are not allowed.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
HTML 4.01 Frameset
This DTD is equivalent to HTML 4.01 Transitional, but allows frameset content.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN" "http://www.w3.org/TR/html4/frameset.dtd">
Recommended tutorial: "html video tutorial"
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