是用于开发Autocad图纸管理系统用到的重要控件，及开发说明和应用-Autocad drawings for development of management systems used in the important controls, and the development and application instructions

Each entity is a AutoCAD drawing has a unique identifier, this is a hexadecimal number, which is stored in a character string in DDVue. MicroStation DGN drawings also have these handles but are calledElement ID instead