ObjectARX protocol extension is a flexible mechanism that can be used to add functionality to existing ObjectARX classes at runtime. Protocol extension allows you to add functions to an existing class without redefining the class and recompiling the application. (See Protocol Extension.)
The AcDbEntity class is associated with a default protocol extension class to provide base class support for the MATCHPROP command. With the default protocol extension class, you can copy color, layer, linetype, and linetype scale properties from one entity to another. It is recommended that you implement AcDbMatchProperties as a protocol extension class for all custom objects derived from AcDbEntity to provide full support for MATCHPROP. If the default protocol extension class is overridden with AcDbMatchProperties, it must include functions to copy the base class properties as well.