Element Wildcards : any « XML Schema « XML Tutorial

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Suppose you want to specify that your element can contain any of the elements. 
Declarations that allow you to include any element from a namespace are called element wildcards. 
To declare an element wildcard, use the <any> declaration: 

<any minOccurs="non negative number" 
     maxOccurs="non negative number or unbounded" 
     namespace="allowable namespaces" 
     processContents="lax or skip or strict"> 

You are not allowed to create global <any> declarations. 
The namespace attribute allows several values, shown in the following table: 

##any allows elements from all namespaces to be included as part of the wildcard 
##other allows elements from namespaces other than the targetNamespace to be included as part of ##targetNamespace Allows elements from only the targetNamespaceto be included as part of the wildcard 
##local allows any well-formed elements that are not qualified by a name space to be included as part of the wildcard 
Whitespace-separated list of allowable namespace URIs allows elements from any listed namespaces to be included as part of 
  the wildcard. Possible list values also include ##targetNamespace and ##local. 


To allow for any content to be used within an element, you have to use the any element:

<xsd:element name="contact">
  <xsd:complexType mixed="true">
   <xsd:sequence>
    <xsd:any maxOccurs="unbounded" processContents="skip"/>
   </xsd:sequence>
  </xsd:complexType>
</xsd:element>