anchor.diff:  https://elasticsearch-dsl.readthedocs.org/en/latest/persistence.html#doctype[persistence
   layer] for working with documents as Python objects in an ORM-like fashion:
   defining mappings, retrieving and saving documents, wrapping the document data
  -in user-defined classes.
  -
  -
  -[discrete]
  -=== License
  -
  -Licensed to Elasticsearch B.V. under one or more contributor
  -license agreements. See the NOTICE file distributed with
  -this work for additional information regarding copyright
  -ownership. Elasticsearch B.V. licenses this file to you under
  -the Apache License, Version 2.0 (the "License"); you may
  -not use this file except in compliance with the License.
  -You may obtain a copy of the License at
  -
  -http://www.apache.org/licenses/LICENSE-2.0
  -
  -Unless required by applicable law or agreed to in writing,
  -software distributed under the License is distributed on an
  -"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  -KIND, either express or implied.  See the License for the
  -specific language governing permissions and limitations
  -under the License.
  +in user-defined classes.
positive.code: For **Elasticsearch 7.0** and later, use the major version 7 (`7.x.y`) of the
  library.
  
  For **Elasticsearch 6.0** and later, use the major version 6 (``6.x.y`) of the
  library.
  
  For **Elasticsearch 5.0** and later, use the major version 5 (`5.x.y`) of the
  
negative.code:     elasticsearch>=2,<3
  
  If you have a need to have multiple versions installed at the same time older
  versions are also released as `elasticsearch2` and `elasticsearch5`.
  
  
  [discrete]
  