> It is not correct to say that, since XHTML is some kind of a "special"
>  XML file with some limited number of tags defined, if one uses only
> those specific tags and specifies XML output, so the ouput will be
> XHTML?

There's an appendix in the XHTML specification that recommends how XHTML
should be formatted so that it works in legacy browsers. For example an
empty p element should be serialized as <p></p>, while an empty br element
should be serialized as <br />.

If you ignore that appendix, then serializing using the XML output method
works fine.

Michael Kay
http://www.saxonica.com/