:process process This lets you restrict tracing of a function to a particular process. If process evaluates to t , then the function is traced from within all processes (this is the default). Otherwise, the function is only traced from within the process that process evaluates to.
:when form This lets you invoke the tracing facilities on a traced function selectively. Before each call to the function, form is evaluated. If form evaluates to nil , no tracing is done. The contents of hcl:*traced-arglist* can be examined by form to find the arguments given to trace.