Source emphasis is the type of emphasis provided when a context menu is displayed. It appears as a dotted box with rounded corners that surrounds the item for which the context menu is requested, or the item that is being dragged.
To provide source emphasis for container items issue the CM_SETRECORDEMPHASIS message with the following values:
You can provide source emphasis for the entire container by setting param1 to NULL.
To remove source emphasis follow the same procedure outlined above, but set the usChangeEmphasis parameter in param2 to FALSE instead of TRUE.