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Interface implemented by all commands used to create a toolbarbutton or menu item. Implementations should be stateless. The command class implements the controller part of an action. One command can appear multiple times on the user interface and should therefore be stateless.
Samples of commands: OpenReportCommand, SaveReportCommand, ExitCommand
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A CommandGroup can contain a set of commands belonging together.
Sample of a command group: Align Left/Center/Right etc. form a group. The group itself can be specified to be of type popup or normal to change the appearance type in the menubar or toolbar.
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Central class to register command groups using a key. This class is used to create a menubar, toolbar or popup menu from the previously defined key.
e.g a command group containing all commands destined for the toolbar can be registerd using the key "Toolbar" (the key is completely user defined and has no special meaning).
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