XHTML was developed by the W3C. This article is presented from the perspective of a web developer and is simplified greatly. If you want an "official" or more in-depth (thus more heavy reading) be sure to check out the W3C's tutorials and documentation concerning XHTML.
Before you begin, you should be reasonably familiar with HTML and CSS and have a general understanding of the Internet and its principles. XHTML is based very closely on HTML. If you would like to familiarise yourself with HTML, check out EchoEcho's HTML Tutorial prior to continuing.
This new version of HTML is very easy to pick up and can generally be learnt and fully comprehended in a matter of a few hours. Do not be afraid of learning XHTML! It is very straight forward!
XHTML is a reformulation of HTML 4.01 with XML
XHTML stands for Extensible HyperText Markup Language and is a reformualtion of HTML 4.01 with XML 1.0.
This means that HTML 4.01 has been redesigned with XML.
The new standard for web documents
HTML is the foundation of formatting documents on the Web and is considered the lingua franca of the Internet. HTML can be hand coded with simple text editors or written with the aid of a HTML Editor, such as Dreamweaver, to speed up the process.
HTML is the building block of web pages. Everything starts and is based around this simple markup language.
XHTML is the newest version of HTML and will eventually replace HTML 4.01. XHTML is based on HTML and relies on it for definitions of tags. IE, the XHTML Documentation does not decribe the properties of the BR tag, rather, you will need to look in the HTML documentation for a description of the BR tag.
Includes many features of XML
XHTML is classified as an XML Application. Thus many features of XML are included in it. XHTML has more powerfull support for XML technologies. The biggest difference between XHTML and HTML is a stricter syntax, as you will discover in the following chapters.
An official W3C recommendation
XHTML is a W3C Recommendation. This means that it is a standard language and is supported by all recent browsers. The World Wide Web Consortuim is a forum of many companies, developers and organisations, headed by Tim Berners-Lee that work together to "lead the web to its full potential". They are involved in many projects for devloping the Internet's technologies.