Probably a stupid question . . .
The MIME type in my php.ini file is set to text/html:
default_mimetype = "text/html"
But, because I use XHTML 1.0 Strict, the MIME type of my web pages is set to text/xml:
<meta http-equiv="content-type" content="text/xml; charset=utf-8" />
I should therefore change the php.ini MIME type to text/xml, right?