XHTML (Extensible Hypertext Markup Language) is one of the first markup languages defined using XML.
W3C is a consortium of commercial and educational institutions that oversees research and promotes standards in all areas related to the World Wide Web.
XHTML extends HTML 4, providing more interoperability for Web documents. For instance, XHTML documents can use scripts that rely on either the HTML or the XML document object models. While FrontPage 2003 has no specific XHTML features, it does support XHTML. By default the FrontPage 2003 settings are correct for working with XHTML. However, if you have customised them in any way, you should change them so that they conform to the XHTML standards.
To ensure the values are set correctly, on the Tools menu, click "Page Options", and then click the Code Formatting tab. XHTML requires that you create all tags and attributes by using lowercase characters. Therefore, you should ensure that the following check boxes are selected:
1. Tag names are lowercase
2. Attribute names are lowercase
On the Code Formatting tab, ensure that the "Omit end tags" check box is deselected because end tags are required.
After you've checked these settings you'll be fine with XHTML in FP2003