changes, or cancels a request to execute a callback command if an
unexpected loss of connection to the database occurs. With a
callbackCommand parameter, the request
is established, or the command string of an already existing
request is replaced. With no callbackCommand parameter, a prior request is
The callback command string is executed from the Tcl idle
loop. That is the normal idle state of an application written
with Tk. In non-Tk Tcl shells, you can execute
to cause the idle loop to be entered.
The handle to watch for connection losses.
If present, provides the command string to execute when connection loss is detected.