ISO/IEC 19757-8:2008 specifies a mechanism that allows users to assign locally meaningful names to XML elements, attributes, entities and processing instructions, without having to completely rewrite the Document Type Definition (DTD) or schema against which they are to be validated. In addition, ISO/IEC 19757-8:2008 provides an XML-based format for declaring the replacement text for entity references and provides a mechanism that allows users to define default values for both element content and attribute values.