Annotation is a human-readable note (comment) of a schema or its part.
It may contain the processing information (see example - xs:appinfo) as well.
Next content is not specified (limited) - see example (bind, class, ...)
<xs:annotation>
<xs:documentation xml:lang="en">Top level element.</xs:documentation>
<xs:documentation xml:lang="fr">Element racine.</xs:documentation>
<xs:appinfo source="http://example.com/foo/">
<bind xmlns="http://example.com/bar/">
<class name="Book"/>
</bind>
</xs:appinfo>
</xs:annotation>