Process models define model callbacks that client sequence files can override, such as the PreUUT or TestReport callbacks. Because a model plug-in is a model file, it can also define model callbacks that client sequence files can override.

The model plug-in sequence file must include the model callback sequence so the plug-in can invoke the callback sequence. The process model must also include a copy of the callback sequence for TestStand to display the callback sequence in the Sequence File Callbacks dialog box so you can conveniently override the process model callback sequences in client sequence files.

The following table outlines ways in which you can implement callbacks and the resulting behavior for each technique. The table uses the term defined to mean that the file contains the callback sequence and the term invoked to mean that other sequences in the file call the callback sequence. If TestStand recognizes the callback at edit time, the callback appears in the Sequence File Callbacks dialog box and uses a green icon in the Sequences pane.

Description of Callback Configuration Resulting Behavior
Defined and invoked only in the process model Client sequence can override the callback, and the callback is recognized at edit time.
Defined and invoked only in the process model plug-in (Not Recommended) Client sequence can override the callback, but the callback is not recognized at edit time.
Defined in the process model and the process model plug-in but invoked only in the plug-in If the client sequence file defines the callback, the client sequence file overrides the plug-in implementation of the callback. Otherwise, TestStand invokes the plug-in definition of the callback. The process model definition of the callback does not override the plug-in definition. The callback is recognized by the client sequence file at edit time.
Defined and invoked in the process model and the process model plug-in If the client sequence file defines the callback, the client sequence file overrides the process model and process model plug-in implementations. Sequences in the process model and the plug-in invoke the process model and plug-in instances of the callback, respectively. The process model definition of the callback does not override the plug-in definition or vice versa. The callback is recognized by the client sequence file at edit-time.