# Extending the content model of an XML document

You can use the XML schema `any` element to extend the content model of an XML document.

For example, you have an XML schema file called Book.xsd which contains a complex type called BookType. BookType contains 4 elements (title, author, year, and ISBN) and one `any`element. The namespace for the `any` element is `##any`. This means that in an instance document, you can insert any XML element to extend the definition of the BookType.

You can also provide a more specific namespace. For example, you have another schema called My_Book.xsd, which contains a complex type called My_BookType. My_BookType contains 4 elements (title, author, year, and ISBN) and one `any` element, but in this case the namespace for the BookType element is www.wesley.com. This means that in an instance document, you can insert any XML element to extend the definition of the BookType, provided that they belong to the namespace http://www.wesley.com.

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