[security-services] Validation of simple attribute value fails?

I had a brief exchange with Chris McLaren on this, but I think I need to
open it up wider.

I don't think the current core schema will validate a simple
AttributeValue of string type such as:

<?xml version="1.0" encoding="UTF-8"?>
	<Attribute
xmlns="http://www.oasis-open.org/committees/security/docs/draft-sstc-sch
ema-assertion-21.xsd"
		xmlns:xsd="http://www.w3.org/2001/XMLSchema"
 		xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	
xsi:schemaLocation="http://www.oasis-open.org/committees/security/docs/d
raft-sstc-schema-assertion-21.xsd
draft-sstc-schema-assertion-21.xsd"
		AttributeName="foo" AttributeNamespace="http://osu.edu">
	<AttributeValue xsi:type="xsd:string">bar</AttributeValue>
</Attribute>

I'm pretty sure that's supposed to be valid, but the schema doesn't
allow AttributeValue to be of type anyType, it specifies a complexType
of saml:AttributeValueType and then defines that as an element sequence.

Chris' recent examples on usage, which I think everybody was happy with,
assumed that xsd:string was a legal xsi:type value, but it's not in this
case. I validated (or rather didn't) using XMLSpy 4 and using the XSV
tool.

Based on my understanding, leaving AttributeValue entirely untyped in
the schema (or explicitly saying anyType) is the intended goal here.

Chris, am I still wrong, and if so, why doesn't that validate?

-- Scott