The terms – XML, HTML and XHTML - refer to the markup language used to write the web pages. Many of us would have heard of HTML (Hypertext Markup Language), invented by Tim Berners-Lee, and used since the early days of internet. XML (Extensible Markup Language) is a meta-language, used to create other markup languages. The traditional HTML was later recast to use the rules of XML and that resulted in a new XML application, called XHTML (Extensible Hypertext Markup Language). Because XHTML rules are strict and unforgiving, not conforming to them when attempting to modify the template would result in error messages. So, what are these rules that Bloggers like us should take note of?