An HTML Document starts with a DTD Declaration. DTD is the acronym for Document Type Definition. It is commonly referred to as Doctype in HTML. It is used by a web browser to determine which rendering mode is being used by the HTML Document.
Another purpose, for which the Doctype is used, is that the markup validators have to determine the rules against which they will verify the HTML document. The most commonly used Doctype is HTML 4.01.
The Doctype HTML 3.2 and Doctype HTML 2.0 are old declrations and lack support for many of the common features. A person can easily choose a Doctype for his HTML document by keeping in mind the features offered by the different type of Doctypes.
Step 1: Doctype HTML 4.01 Strict
The most commonly used Doctype in HTML is 4.01. This doctype declares the document as HTML 4.01 Strict Document. This version stresses upon the overall structure of the document rather than the look of the document.
Step 2: Doctype HTML 4.01Transition
Another commonly used doctype in HTML is 4.01 Transition. This doctype is the same as the HTML 4.01 strict but it gives some added features which are not present in the HTML 4.01 strict declaration. The following features are not present in HTML 4.01 Strict, however they are present in the
Doctype HTML 4.01 Transition.
Step 3: HTML 4.01 frameset
Those HTML Documents in which framesat used, the HTML 4.01 frameset is usually set as the doctype here.
Step 4: Doctype HTML 3.2
The Doctype HTML 3.2 is an old Doctype Declaration. It is supported by almost all of the browsers, however it is rarely used now. This Doctype declaration lacks support for many features such as frames and style sheets.
Step 5: Doctype HTML 2.0
This Doctype Declaration is another old declaration. It is also supported by almost all of the browsers, however it lacks support for many of the features. These features include tables, frames, presentation attributes and elements.