Case sensitivity of parameter member names

I'm calling a XML-RPC remote procedure and I'm finding that the
application is case sensitive with respect to member names in my
methodCall.  I was wondering if the XML-RPC spec says anything
specific about case sensitivity, or if it's simply up to the
discretion of the application?

For example in the following I find that using 'UserName' instead of
'username' fails with this app.

<methodCall>
  <methodName>getData</methodName>
  <params>
    <param>
      <value><struct>
        <member>
          <name>username</name>
          <value><string>foo</string></value>
        </member>


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