XML Schema - unspecified elements and attributes

XML Schema allows to use some elements that are not known prior to its use.

Example:

<xs:complexType name="descType" mixed="true">
 <xs:sequence> 
  <xs:any namespace="http://www.w3.org/1999/xhtml" 
          processContents="skip" minOccurs="0" maxOccurs="unbounded"/>
 </xs:sequence> 
</xs:complexType> 

Use xs:anyAttribute for attributes.