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

XSD The <any> Element

The <any> element enables us to extend the XML document with elements not specified by the schema!

The <any> Element

The <any> element enables us to extend the XML document with elements not specified by the schema.

The following example is a fragment from an XML schema called "family.xsd". It shows a declaration for the "person" element. By using the <any> element we can extend (after <lastname>) the content of "person" with any element:

<xs:element name="person">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="firstname" type="xs:string"/>
      <xs:element name="lastname" type="xs:string"/>
      <xs:any minOccurs="0"/>
    </xs:sequence>
  </xs:complexType>
</xs:element>

Now we want to extend the "person" element with a "children" element. In this case we can do so, even if the author of the schema above never declared any "children" element.

Look at this schema file, called "children.xsd":

<?xml version="1.0" encoding="ISO-8859-1"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://www.w3schools.com"
xmlns="http://www.w3schools.com"
elementFormDefault="qualified">

<xs:element name="children">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="childname" type="xs:string"
      maxOccurs="unbounded"/>
    </xs:sequence>
  </xs:complexType>
</xs:element>

</xs:schema>

The XML file below (called "Myfamily.xml"), uses components from two different schemas; "family.xsd" and "children.xsd":

<?xml version="1.0" encoding="ISO-8859-1"?>

<persons xmlns="http://www.microsoft.com"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:SchemaLocation="http://www.microsoft.com family.xsd
http://www.w3schools.com children.xsd">

<person>
<firstname>Hege</firstname>
<lastname>Refsnes</lastname>
<children>
  <childname>Cecilie</childname>
</children>
</person>

<person>
<firstname>Stale</firstname>
<lastname>Refsnes</lastname>
</person>

</persons>

The XML file above is valid because the schema "family.xsd" allows us to extend the "person" element with an optional element after the "lastname" element.

The <any> and <anyAttribute> elements are used to make EXTENSIBLE documents! They allow documents to contain additional elements that are not declared in the main XML schema.