XHTML Validation

An XHTML document is validated against a Document Type Definition (DTD). Before an XHTML file can be properly validated, a correct DTD must be added as the first line. The Strict DTD includes elements and attributes that have not been deprecated or do not appear in framesets: 

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

The Transitional DTD includes everything in the strict DTD plus deprecated elements and attributes: 

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

The Frameset DTD includes everything in the transitional DTD plus frames as well: 

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

This is a simple XHTML document: 

 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
   "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
 <html>
  <head><title>simple document</title></head>
  <body><p>a simple paragraph</p></body>
 </html>

Test the XHTML with the W3C validator by entering the page address: 
      

Demonstration
The following demonstration shows how the script of HTML is displayed on the Web.