ATTR_CALLBACK_MODE

Data Type: integer
Description: Specifies the callback mode for the callback. See the documentation for InstallWinMsgCallback() for more details.
Values:
VAL_MODE_IN_QUEUELabWindows/CVI's handler sees the message and a call to your callback is placed in LabWindows/CVI's standard UI event queue.
VAL_MODE_INTERCEPTThe callback is executed before LabWindows/CVI sees the message. You would use this mode if you needed to adjust or swallow messages before LabWindows/CVI's handler sees them.