Xhtml

The XHTML 1.0 specification is basically an attempt by W3C to provide a new standard of http markup, with much greater compatibility over various ‘user agents’, without breaking anything.

The Web Developers’ Virtual Library says it well:

Portability: By the year 2002 as much as 75% of Internet access could be carried out on non-PC platforms such as palm computers, televisions, fridges, automobiles, telephones, etc. In most cases these devices will not have the computing power of a desktop computer, and will not be designed to accommodate ill-formed HTML as do current browsers (bloated with code to handle sloppy or proprietary HTML).