This section describes the container objects used in AutoCAD ® database operations: symbol tables, dictionaries, groups, and xrecords. As part of any drawing, AutoCAD creates a fixed set of symbol tables and the named object dictionary, which contains two other dictionaries, the MLINE style and GROUP dictionaries. The section examples demonstrate how to add entries to symbol tables, dictionaries, and groups, and how to query the contents of these containers using iterators. They also show how to create and use your own dictionaries and xrecords to manage application data and objects. For a description of the extension dictionary of an AcDbObject object, see Database Objects.