Calculations

<instance>
  <my:order>
    <my:item>
      <my:amount />
      <my:discount />
    </my:item>
  </my:order>
</instance>
<bind nodeset="my:item/my:discount" 
      calculate="../my:amount * 0.1"
      type="xsd:decimal" />

• bind element in the model associates an XPath calculation with particular elements in the instance

• nodeset attribute chooses the nodes whose values are calculated

• calculate attribute contains the XPath expression that's evaluated to give the values for those nodes

• Optional type attribute specifies schema type for the expression result

• Side-effect free (unlike JavaScript)