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

XSD The <anyAttribute> Element

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

The <anyAttribute> Element

The <anyAttribute> element enables us to extend the XML document with attributes 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 <anyAttribute> element we can add any number of attributes to the "person" element:

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

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

Look at this schema file, called "attribute.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:attribute name="gender">
  <xs:simpleType>
    <xs:restriction base="xs:string">
      <xs:pattern value="male|female"/>
    </xs:restriction>
  </xs:simpleType>
</xs:attribute>

</xs:schema>

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

<person gender="female">
<firstname>Hege</firstname>
<lastname>Refsnes</lastname>
</person>

<person gender="male">
<firstname>Stale</firstname>
<lastname>Refsnes</lastname>
</person>

</persons>

The XML file above is valid because the schema "family.xsd" allows us to add an attribute to the "person" 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.