specify root for xsd validation

[Jan Nowakowski]

Hi,
I have a xsd file which allows multiple elements to be the root element of a correct xml, i.e.

<xs:schema>
<xs:element name="a" type="xs:string" />
<xs:element name="b" type="xs:integer" />
</xs:schema>

Is it possible to validate an xml file against this schema but also tell the validator that the root of the xml file should be "a" but not "b" ?
Something like

validator.setRootElement("a") 

so that an xml like:

<b>
123
</b>

would fail the validation but

<a>
some string
</a>

would pass