
The W3C, which is the organization that co-ordinates standardisation of Web protocols, has defined three types of XHTML documents. This is based on the XML Document Type Definition (DTD) that is used by the document. The XHTML DTDs are:
Strict : Used when the XHTML document is devoid of all formatting tags like <font> and Cascading Style Sheets (CSS) are used for controlling all presentation aspects.
Transitional : This XHTML DTD allows use of presentation tags in the document. This is a safer mode since most of our pages contain many presentation elements.
Frameset : Used for XHTML documents that describes frames.
1)The first line in the HTML document may be the XML processing instruction:
<?xml version="1.0" encoding="iso-8859-1"?>
2) The second line in the XHTML document should be the specification of the document type declaration (DTD) used. The document type declaration for transitional XHTML documents is:
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
The declarations for the strict XHTML DTD is:
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
The declarations for the frameset XHTML DTD is:
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">
3)The starting tag <html> should be modified to include namespace information. The modification is:
<html xmlns="http://www.w3.org/1999/xhtml" lang="EN">
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