docs: def _init_default_values(self):
          """Set default initial values
  
          The default values are hard-coded for backwards compatibility
          and for several functionalities in dclab.
          """
          # Do not filter out invalid event values
          self["filtering"]["remove invalid events"] = False
          # Enable filters switch is mandatory
          self["filtering"]["enable filters"] = True
          # Limit events integer to downsample output data
          self["filtering"]["limit events"] = 0
          # Polygon filter list
          self["filtering"]["polygon filters"] = []
          # Defaults to no hierarchy parent
          self["filtering"]["hierarchy parent"] = "none"
          # Check for missing min/max values and set them to zero
          for item in dfn.scalar_feature_names:
              appends = [" min", " max"]
              for a in appends:
                  self["filtering"][item + a] = 0