Extensible hypertext markup language

XHTML stands for eXtensible HyperText Markup Language. XHTML is a reformulation of HTML forms using the XML paradigm. [1] XHTML is a markup language for the router and the development of HTML which has a capacity of more or less similar to HTML, but with a more strict syntax rules. HTML is an application of SGML (Standard Generalized Markup Language) that is very flexible, whereas XHTML is an application of XML, SGML derivative that is more limited.

Reasons for Using HTML
XHTML improve the deficiencies in the HTML.
XHTML can be run on multiple platforms, allowing us to open the site either through the PDA and mobile phones.
Writing
XHTML is not too different from the HTML 4.01 standard. If you already have the ability HTML 4.01 it will help to launch XHTML. XHTML requires that the writing of tags with lowercase (lowercase) and always closed using the closing tag. Some rules in XHTML
As mentioned previously, XHTML is an improved version of HTML. For that, there are some rules that are more stable and consistent program.

Each tag must be written in lowercase.
Opening and closing tags on the correct nest.
Attribute tags are written with lowercase letters and using quotation marks.
Providing cover for each tag.
Source : www.wikipedia.com