controls restricted to certain bound types

Hi,

I have a question about the 1.0 spec.  It says that inputs, ranges and 
uploads all have limitations as to the types of data that they can bind 
to.  xf:input is spelled out pretty clearly...it can only bind to 
simpleContent that is NOT xsd:base64Binary or xsd:hexBinary or derived 
from them.

However upload and range do NOT have the simpleContent rule.    For 
example, upload says, "This form control can only be bound to datatypes 
xsd:anyURI, xsd:base64Binary or xsd:hexBinary, or types derived by 
restriction from these."  Is this just simpleContent restriction or does 
this include complexContent restriction?  Also why can't I bind to a 
node with a complex type that uses simpleContent extension?  Like:

<xs:complexType name="myType">
   <xs:simpleContent>
     <xs:extension base="xs:anyURI">
       <xs:attribute name="filename" type="xs:string"/>
       <xs:attribute name="mediatype" type="xs:string"/>
     </xs:extension>
   </xs:simpleContent>
</xs:complexType>

Any clarification appreciated.

Thanks,
--Aaron