may specify (by omission) the default set. This set is
exactly like any other set, except that it is automatically
cancelled after the occurrence of any event. It may be
explicitly named by using the empty string, (ie,
may also specify (by omission) the default target. This
target, whose name is also the empty string, has the special
propery that it always refers to ``the statement immediately
following the next wait statement.'' That is, if the target of
any event is the default target, the occurrence of that event
just causes execution to continue starting with the statement
following the wait statement.
all is used with the ``cancel''
command, all sets (i.e., all pending events) are cancelled.