tying attribute values to data types

[Tim Cronin <tim@13-colonies.com>]

I have an XML doc where an attribute value is used to
tell what type of data the element has. Is there a way 
to validate this via schema?

Here's what the XML looks like

<Datum Type="String"><!-- XML Safe String --></Datum> 
<Datum Type="Color"><!-- named color or RGB hex code --></Datum> 
<Datum Type="Boolean"><!-- YES or NO --></Datum> 
<Datum Type="Number"><!-- any valid number int float signed --></Datum> 
<Datum Type="Font"><!-- has a specific child element format -->
  <Font Size="" Family="" Style="" Weight="" Color=""/>
</Datum> 
<Datum Type="Text">
  <![CDATA[<!-- Free form text -->]]>
</Datum> 
<Datum Type="XML">
  <![CDATA[<!-- valid XML but not part of schema -->]]>
</Datum>