If you're "good", you'll do this.

...but we're not always "good",... like those comments in your Java code, right?

Example:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           targetNamespace="..."
>

<!-- there is one main information annotation for the schema namespace -->
<xs:annotation>
<xs:documentation  xmlns="http://www.w3.org/1999/xhtml">
<p>This schema is used for...</p>
</xs:documentation>
</xs:annotation>

<!-- every element has an annotation -->
<xs:element name="...">
<xs:annotation>
...
</xs:annotation>
...
</xs:element>

<!-- every type has an annotation -->
<xs:complexType name="...">
<xs:annotation>
</xs:annotaiton>
...
</xs:complexType>

<!-- etc. -->

</xs:schema>