The complete XHTML specification is available at XHTML specification at www.w3c.org.
Here is listed a summary of what is needed to be XHTML compliant:
All pages should have the following xml declaration:
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
All open tags must be closed, all tags must stay between < and >.
<HTML> must be converted to <html>.
No standalone <br> tag is allowed; <br/> must be used.
<td rowspan=3> must be converted to <rowspan="3">.
The differences listed here are the most significant differences between HTML and XHTML, there are other, minor differences. For a complete list, refer to the XHTML specification.