docs: def range(cls, field, from_value=None, to_value=None, include_lower=None, include_upper=None):
          '''
          http://www.elasticsearch.org/guide/reference/query-dsl/range-filter.html
  
          Filters documents with fields that have terms within a certain range. Similar to range query, except that it acts as a filter. Can be placed within queries that accept a filter.
          '''
  
          instance = cls({'range': {field: {}}})
          if from_value is not None:
              instance['range'][field]['from'] = from_value
          if to_value is not None:
              instance['range'][field]['to'] = to_value
          if include_lower is not None:
              instance['range'][field]['include_lower'] = include_lower
          if include_upper is not None:
              instance['range'][field]['include_upper'] = include_upper
  
          return instance