t>
<dd><p>This creates a callback that is called whenever the signal posts
the given message.  This is a little easier than having to write a
function that must check the message each time it is called.
Although the <cite>message</cite> here is a string, if a message posted to the
signal is an array, then only the first element of that array is
used to match against message.  That way, if a message contains an
identifier plus arguments, the hook will match the identifier and
still get called with the comple