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

XML Schema documentation Element

Definition and Usage

The documentation element is used to enter text comments in a schema. This element must go inside an annotation element.

Element Information

Parent elements: annotation

Syntax

<documentation
source=URI reference
xml:lang=language>

Any well-formed XML content

</documentation>

Attribute	Description
source	Optional. Specifies the source of the application information
xml:lang	Optional. Specifies the language used in the contents

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