text/xml can be a problem. Some caching proxies will rewrite the character encoding of
text/* files. In the case of an XML file, this could make the actual character encoding differ from the character encoding declared within the document itself. And besides, I think
text/xml has been deprecated.
So always use
application/xml for generic XML documents, and
application/*+xml for specific documents which have their own registered MIME types (
application/xul+xml for XUL, for example).
application/ecmascript, which is more strictly defined).
text/plain or even make something up altogether.