Although this exercise used only one signal of the input record, many
applications will use two or more signals simultaneously. The Signal
list initially contains the signal numbers of all available signals; as noted
above, the signal list can be passed to an application listed in the menu file
as a set of command-line arguments in place of the string `$SIGNALS'.
Although you can type into the Signal list field directly to change it,
you can also do so using the mouse. Pointing to a signal, hold down the
key while clicking left to add it to the signal list, or hold
down the Meta key while clicking left to delete its first
occurrence from the signal list. (Most keyboards do not have a key
labelled Meta. On most Sun keyboards, the Meta keys look like
this: 
; they flank the space bar. On most
other keyboards, the 
key is equivalent to Meta.)