NIL - no tracing information given, and translated definitions side-effect the environment (usually by storing assertions in some database or calling the target representation system)
<a stream> - a trace of the translation process will be output to the specified stream. Use *translation-output-stream* for creating files of the translation.
:PRINT-ONLY - translations will be output to *trace-output*, but will not have any side effects
<a list> - a conjunction of a stream, :PRINT-ONLY, and/or NIL
<anything else> - translations will be output to *trace-output*
The current value of *ONTO-TRACE* is NIL