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

XML Schema appInfo Element

Definition and Usage

The appInfo element specifies information to be used by the application. This element must go within an annotation element.

Element Information

Parent elements: annotation

Syntax

<appInfo
source=anyURL
>

Any well-formed XML content

</appInfo>

Attribute	Description
source	Optional. A URI reference that specifies the source of the application information

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