XHTML Document Type Definitions
By referencing the Document Type Definition (DTD), DOCTYPE definition line in an XHTML document specifies the document type .
The syntax and legal elements of an XHTML document are specified by DTD. The three types of documents are defined as follows:
By using this type a strictest rule is applied on the document. There shoulnot be any presentational tags in XHTML.
To display the data should use cascading style sheets. The attributes and elements which are not deprecated or do not appear in framesets are included in strict DTD.
This document type is used when document contains presentational tags. For the browsers which do not support Cascading Style Sheets, This document type seems to be useful. The Transitional DTD includes all that included in the strict DTD and also the deprecated elements and attributes.
When we make use of frames to split the browser window then this document type can be used. This includes all that which is present in The transitional DTD and also the frames