built-in shelf
#process-output identifies the default output destination provided to OmniMark by the system.
In earlier releases of OmniMark, #process-output was called #console ; although this
keyword can still be used to perform the same function, its use is deprecated.
The declare #process-output has declarations can be used to change some of the characteristics of
the #process-output stream. Note that #process-output never allows referents, so to declare that this stream has referents-allowed
or referents-not-allowed is an error.