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Importance of HTML DOCTYPE

Source: Internet
Author: User
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Definition and usage

<! DOCTYPE> Declaration must be the first line of the HTML document, located before the <! DOCTYPE> the declaration is not an HTML Tag; it indicates the web browser's instructions on which HTML version the page is written.

In HTML 4.01, <! DOCTYPE> declare to reference DTD because HTML 4.01 is based on SGML. The DTD specifies the markup language rules so that the browser can correctly render the content.


DOCTYPE

HTML 4.01 Strict

This DTD contains all HTML elements and attributes, but does not include explicit and obsolete elements (such as font ). Framesets is 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 explicit and obsolete elements (such as font ). Framesets is 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 the content of the framework set.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN" "http://www.w3.org/TR/html4/frameset.dtd">

If doctype is not added to html, a bug may occur in different browsers. Therefore, adding doctype to html is crucial.



Reference: http://www.w3school.com.cn/tags/tag_doctype.asp








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