on [<modes>]status_update [<serial#>] [-|^]<match> { <action> }
This hook is triggered whenever the status bar of a visible window in dumb mode is updated.
| $0 | Refnum of the window whose status bar was updated |
| $1 | Which status bar has changed, 0 or 1 |
| $2- | The actual status bar that has been updated |