For example, a schema author can build a schema that borrows from a previous schema, but overrides it where new unique features are needed. XML Schema allows the author to determine which parts of a document may be validated, or identify parts of a document where a schema may apply. XML Schema also provides a way for users of ecommerce systems to choose which XML Schema they use to validate elements in a given namespace, thus providing better assurance in ecommerce transactions and greater security against unauthorized changes to validation rules. Structures specifies the XML Schema definition language, which offers facilities for describing the structure and constraining the contents of XML 1.0 documents, including those which exploit the XML Namespace facility. Schemas may also provide for the specification of additional document information, such as normalization and defaulting of attribute and element values.
Schemas have facilities for self-documentation.
Structures formalism to express syntactic, structural and value constraints applicable to its document instances. Structures formalism allows a useful level of constraint checking to be described and implemented for a wide spectrum of XML applications. However, the language defined by this specification does not attempt to provide all the facilities that might be needed by any application. Some applications may require constraint capabilities not expressible in this language, and so may need to perform their own additional validations. Datatypes is part 2 of the specification of the XML Schema language.