'Return XML string based on settings accumulated via method calls'

@property
def xml(self):

    if self._empty:
        return ('<Types    xmlns="%s"/>\n' % NS.OPC_CONTENT_TYPES)
    xml = ('<Types    xmlns="%s">\n' % NS.OPC_CONTENT_TYPES)
    for (extension, content_type) in self._defaults:
        xml += a_Default().with_extension(extension).with_content_type(content_type).with_indent(2).without_namespace().xml
    for (partname, content_type) in self._overrides:
        xml += an_Override().with_partname(partname).with_content_type(content_type).with_indent(2).without_namespace().xml
    xml += '</Types>\n'
    return xml
