XML Schema: Element with attributes containing values from other attributes

XML Schema: Element with attributes containing values from other attributes

Not sure this is possible with XSD, but still the question is here.
So I have the following code in my xml:
<formats>
<format name="TableText">
<item name="halign">left</item>
</format>
</formats>
<styles>
<style name="Style">
<item name="format">TableText</item>
</style>
</styles>
What I want to achieve is that when the user starts typing content of a
format (<item name="format">TableText</item>), he would only be able to
enter what he had in a name attribute of a format tag (<format
name="TableText">)