If someone just says that this is the high time when you should convert your site from HTML to XHTML - you can halt or not. But if he can say this with proper logic then you must be going through his decision - adaptibility is another thing. So at first you must know basically what XHTML is. XHTML is really more similar to HTML than it is different. The "changes" aren't really changes, but just a set of stricter standards to obey. XHTML stands for Extensible HyperText Markup Language. XHTML is a cross between HTML and XML. Any XHTML document will be valid HTML and valid XML, which means it can be opened in any XML editor.