Schema: element's content should be different depending on it's position

Hello All,

I want to make schema in wich element's content should depend on element's
position.
i.e:

<request>
	<type>user</type>
	<login>link</login>
</request>

---OR---

<request>
	<type>group</type>
	<groupName>link</groupName>
</request>
------------

I am using <choice> now:
Example:


<choice>
	<sequence>
		<element name="type" minOccurs="1" maxOccurs="1">
			<!-- Only user allowed here! -->
		</element>
		<element name="login" minOccurs="1" maxOccurs="1"
type="string" />
	</sequence>
	<sequence>
		<element name="type" minOccurs="1" maxOccurs="1">
			<!-- Only group allowed here! -->
		</element>
		<element name="groupName" minOccurs="1" maxOccurs="1"
type="string" />
	</sequence>
</choice>

What can I do with "type"?

Thanks.

====================
Kazakevich Ilya,
DevExperts
====================