constraint by factoring the symbol out of the alternatives, e.g.,
@code{["foo" &or [first case] [second case] ...]}.
-Most needs are satisfied by these two ways that bactracking is
+Most needs are satisfied by these two ways that backtracking is
automatically disabled, but occasionally it is useful to explicitly
disable backtracking by using the @code{gate} specification. This is
useful when you know that no higher alternatives could apply. See the