Introducing child elements in appinfo

Hallo folks,

Following the example of [1]:
<xs:annotation>
 <xs:documentation>A type for experts only</xs:documentation>
 <xs:appinfo>
  <fn:specialHandling>checkForPrimes</fn:specialHandling>
 </xs:appinfo>
</xs:annotation>

I attempted to introduce a custom element/namespace for my own needs
(the ns is declared in the schema root):

<xsd:annotation>
 <xsd:appinfo>
  <bs:defaultFix>/@Alignment</bs:defaultFix>
 </xsd:appinfo>
</xsd:annotation>

MSXML4 gives me "Element bs:defaultFix not defined in DTD/Schema".
What am I missing?

[1] http://www.w3.org/TR/xmlschema-1/#cAnnotations

Thanks for your time,

Manos