XHTML is a stricter form of HTML which combines elements of XML to allow different platforms to more easily display web pages. (cell phones, pdas, etc.) XHTML 1.0 is the latest official standard, and if your site is compliant with "strict," you are using it.Originally Posted by nseidm1
The other doctypes are for various stages of compliance (mostly for use on web sites that are still being converted to XHTML) and for web sites designed specifically for other platforms such as cell phones or pdas. There may also be some sample doctypes for web designers who want to create their own.