======Synopsis:======
[[on]] [<modes>]exec_errors [<serial#>] [-|^]<match> { <action> }

======Description:======
This hook is triggered whenever an [[exec command|EXEC]]ed process produces output to
standard error.

======Parameters:======
|$0    |process number or name of the [[exec command|EXEC]]ed process   |
|$1-   |a line of the process's output to stderr                        |

======Default behavior:======
If you do not suppress this event, the client will format the message
and display it to your screen **UNLESS** you are redirecting the output
of that [[exec]] to somewhere else.

======Examples:======
To distinguish process errors from other window output:
   on ^exec_errors "*" {
      echo [$0 ERR] $1-
   }