Question on xacml 2.0 - multiple action-id Request/Action elements

I have been asked whether a Request/Action element can
contain more than one 
  <Attribute AttributeId="...action:action-id">
element:

For example, what would be wrong with Example 4.1.2 having
the following:

<Action>
  <Attribute 
      AttributeId="urn:oasis:names:tc:xacml:1.0:action:action-id"
      DataType="http://www.w3.org/2001/XMLSchema#string">
    <AttributeValue>read</AttributeValue>
    <AttributeValue>write</AttributeValue>
  </Attribute>
</Action>

Apparently, some have the opinion this is not
allowed. I think that opinion is mistaken, 
because I have not found any reason that this is 
disallowed. Is there anything that forces
us to only have one value for action-id?

	Thanks,
	Rich