Hi there,
I'm no expert, but it does not make sense at all to me.
First of all xhtml should have nothing to do with filenames. It is a URL you are calling and that does not require any such thing as a file extension. Because, it does mat some Universal Resource Locater (URL) into some data response, which can come from a database as well as it can be mapped into a file system tree of *.html files, or into a set of script files i.e. *.php
To the contrary it is wise practice to stay away from extensions as part of the URL. It is better to define the URL name space as
http://www.example.com/a-dir/first-page rather than
http://www.example.com/a-dir/first-page.html. Because, it allows you to change the technology behind the scenes without changing the URL space (i.e. re-implement your site based on a PHP based CMS). By the way
http://www.example.com/a-dir/ (notice the "/" at the end) would be shorthand for give me a directory listing of "a-dir" if this is allowed in the URL space. How this is handled is configured by the web-server (default on most servers is to serve the file
http://www.example.com/a-dir/index.html).
I hope that answers the question.
K<o>