When the interpreter starts, it checks the setting of the special environment variable, RXTRACE. If RXTRACE has been set to ON (not case-sensitive), each time when starting a new Rexx procedure, the interpreter starts in interactive debug mode as if the Rexx instruction TRACE '?R' had been the first interpretable instruction. All other settings of RXTRACE are ignored. RXTRACE is only checked when starting a new Rexx interpreter, it is not checked each time when starting a new Rexx procedure.