From http://www.w3schools.com (Copyright Refsnes Data)

XML Schema annotation Element

Definition and Usage

The annotation element is a top level element that specifies schema comments. The comments serve as inline documentation.

Element Information

Parent elements: Any element

Syntax

<annotation
id=ID
any attributes
>

(appinfo|documentation)*

</annotation>

(The * sign declares that the element can occur zero or more times inside the annotation element)

Attribute	Description
id	Optional. Specifies a unique ID for the element
any attributes	Optional. Specifies any other attributes with non-schema namespace

Example 1

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

<xs:annotation>
  <xs:appInfo>W3Schools Note</xs:appInfo>
  <xs:documentation xml:lang="en">
  This Schema defines a W3Schools note!
  </xs:documentation>
</xs:annotation>

.
.
.

</xs:schema>

Complete XML Schema Reference