1. In a computer system, a memory having stored therein an object-oriented software platform for serving a plurality of currently executing client applications, the platform including a data encapsulation system for encapsulating application data in response to encapsulation requests by the plurality of applications, a data selection system for selecting the application data, which is encapsulated by said data encapsulation system in response to selection requests by the applications, and a command object system comprising: a client-subclassable command object base class, resident in the address space of the memory defined by the platform, the command object base class including: a member function, responsive to creation requests from the plurality of applications, wherein each application resides in a unique application address space different than that of the address space of the platform, and wherein the application data resides in the unique address space of a corresponding application, the member function having means for creating at least one command object for use by a requesting application, the command object being created in the application address space of the requesting application; and a member function, responsive to execution requests from the plurality of applications made via a created command object, for executing a predefined document editing operation on the application data, which is selected by said data selection system.