code: def log_tag(self, tag, code, multiline=False):
          
          if self.tracing:
              if callable(code):
                  code = code()
              tagstr = "[" + str(tag) + "]"
              if multiline:
                  printerr(tagstr + "\n" + displayable(code))
              else:
                  printerr(tagstr, ascii(code))
docs: Logs a tagged message if tracing.