docs: def get_all(self, attr, value, e=0.000001,
                  sort_by="__name__", reverse=False):
          """Get all nested Constant class that met ``klass.attr == value``.
  
          :param attr: attribute name.
          :param value: value.
          :param e: used for float value comparison.
          :param sort_by: nested class is ordered by <sort_by> attribute.
  
          .. versionchanged:: 0.0.5
          """
          matched = list()
          for _, klass in self.subclasses(sort_by, reverse):
              try:
                  if getattr(klass, attr) == approx(value, e):
                      matched.append(klass)
              except:  # pragma: no cover
                  pass
  
          return matched