[XML Schema 1.1] XPath in <alternative> cannot look up or down the tree, correct?

Hi Folks,

I wish to confirm my understanding.

Here's an example that uses the <alternative> element:

<xs:element name="Publication" type="PublicationType">
    <xs:alternative test="____" type="..." />
</xs:element>


It is my understanding that the XPath expression in test="____" must only reference attributes of Publication. It cannot reference ancestors and it cannot reference descendants. 

That is, the XPath in an alternative element cannot look up or down the tree.

Do I have a correct understanding?

/Roger