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4.1.2 Terminology
First, let’s look at the terminology used in this chapter. If you
don’t get a thorough understanding of these terms, you will
probably not understand much of what is said in the rest of this

     A situation, external or internal to the interpreter, which
     it is required to respond to in certain pre-defined manners.
     The interpreter recognizes incidents of several different
     types. The incident will often have a character of
     “suddenness”, and will also be independent of the normal
     control flow.

     Data Structure describing one incident, used as a descriptor
     to the incident itself.

     Names the REXX concept that is equivalent to the incident.

[Raise a Condition:]
     The action of transforming the information about an incident
     into an event. This is done after the interpreter senses the
     condition.  Also includes deciding whether to ignore or
     produce an event.

[Handle a Condition:]
     The act of executing some pre-defined actions as a response
     to the event generated when a condition was raised.

[(Condition) Trap:]
     Data Structure containing information about how to handle a

[(Trap) State:]
     Part of the condition trap.

[(Condition) Handler:]
     Part of the condition trap, which points to a piece of REXX
     code which is to be used to handle the condition.

[(Trap) Method:]
     Part of the condition trap, which defined how the condition
     handler is to be invoked to handle the condition.

[Trigger a Trap:]
     The action of invoking a condition handler by the method
     specified by the trap method, in order to handle a condition.

[Trap a Condition:]
     Short of trigger a trap for a particular condition.

[Current Trapped Condition:]
     The condition currently being handled. This is the same as
     the most recent trapped condition on this or higher procedure

[(Pending) Event Queue:]
     Data Structure storing zero or more events in a specific
     order.  There are only one event queue. The event queue
     contains events of all condition types, which have been
     raised, but not yet handled.

     The pre-defined default way of handling a condition, taken if
     the trap state for the condition raised is OFF.

     The pre-defined default action taken when a condition is
     raised, and the trap state is DELAY.