for an expression that contains no
terminals or nonterminals. This feature is often useful. For example, we
might have</P>

<PRE>   Option =  "push" (. stack[++top] = item; .)
           | "pop"  (. item = stack[top--]; .)
           |        (. MonitorStack(); .) .
</PRE>

<P><B>Syntax error handling</B>. The programmer has to give some hints
in order to allow Coco/R to generate good and efficient error handling.
Firstly, synchronization points have to be specified. A synchronization point
is a location in