By default, the AllowContextMenu property is -1 (exAllowContextMenu),
which indicates that the control's context-menu is allowed. The control's
context-menu is shown once the user right clicks the control. The
AllowContextMenu property on 0 (exDisableContextMenu) disables the control's
context-menu, so the user can't show the control's context-menu when user
right-clicks the control or press the Context key.