This part of ISO/IEC 19757 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 DTD or schema against which they are to be validated. In addition, this part of ISO/IEC 19757 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.