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  • Document type declaration

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    Document type declaration ( Or DOCTYPE )

    What is Doctype ?

    The<!DOCTYPE> is not a HTML tag. It is an instruction to web browser about what version of HTML the page is written in.


    In HTML 4.01, the<!DOCTYPE> declaration refers to a DTD, because HTML 4.01 based on SGML (Standard Generalized Markup Language). So that the browsers render the content correctly.

    It is a top level tag known as a Public Text Identifier

    HTML5 is not based on SGML so its not require any reference for DTD.

    Explanation of Doctype ?

    HTML DOCTYPE statement:-


    <!DOCTYPE HTML PUBLIC " - // W3C DTD HTML 4.01 // EN " " http://www.w3.org/TR/html4/strict.dtd ">
    (A) (B) (C) (D) (E) (F) (G) (H)

    A pair of forward slash characters ("//") is used as delimiters between keyword fields in the FPI (Formal Public Identifier) declaration.

    (A : Top Element):- Its Indicates the top level element type declared in the DTD
    e.g:- For HTML it is <html>.
    For XHTMl it is <XHTML >

    (B : Availability):- field indicates whether the identifier is a publicly accessible object (PUBLIC) or a system resource (SYSTEM) such as a local file or URL. HTML/XHTML DTDs are specified by PUBLIC identifiers.

    (C : Registration) - Indicated by either a plus ("+") or minus ("-"). A plus symbol indicates that the organization name that follows is ISO-registered. A minus sign indicates the organization name is not registered. The IETF and W3C are not registered ISO organizations and thus use a "-".

    (D : Organization] - This is the "OwnerID" - a unique label indicating the name of the entity or organization responsible for the creation and/or maintenance of the artifact (DTD, etc.) being referenced by the DOCTYPE. The IETF and W3C are the two originating organizations of the official HTML/XHTML DTDs.

    (E : Type) - This is the "Public Text Class" - the type of object being referenced. There are many different keywords possible here, but in the case of an HTML/XHTML DTD, it is "DTD" - a Document Type Definition.

    (F : Label) - This is the "Public Text Description" - a unique descriptive name for the public text (DTD) being referenced. If the public text changes for any reason, a new Public Text Description string should be created for it.

    (G : Language) - This is the "Public Text Language"; the natural language encoding system used in the creation of the referenced object. It is written as an ISO 639 language code (uppercase, two letters.) HTML/XHTML DTDs are usually (always?) written in English ("EN".)

    (H : URL) - This is the optional explicit URL to the DTD being referenced.

    Type of Doctype ?

    HTML 2.0 -

    <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0 Level 2//EN"> <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN"> <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"> <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML Level 2//EN">

    HTML 3.0 -

    <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 3.0//EN">

    HTML 3.2 -

    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">

    HTML 4.01 -

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

    HTML 5 -

    <!DOCTYPE HTML>

    XHTML 1.0 -

    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">

    XHTML 1.1 -

    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN">

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