anchor.diff:  similar to a column in a table in a relational database.
   
   The <<glossary-mapping,mapping>> for each field has a field _type_ (not to
  -be confused with document <<glossary-type,type>>) which indicates the type
  +be confused with document type) which indicates the type
   of data that can be stored in that field, eg `integer`, `string`,
   `object`. The mapping also allows you to define (amongst other things)
   how the value for a field should be analyzed.
  
positive.code: // tag::mapping-def[]
  A mapping is like a _schema definition_ in a relational database. Each
  <<glossary-index,index>> has a mapping,
  which defines a <<glossary-type,type>>,
  plus a number of index-wide settings.
  
  A mapping can either be defined explicitly, or it will be generated
  
negative.code: // tag::document-def[]
  A document is a JSON document which is stored in Elasticsearch. It is
  like a row in a table in a relational database. Each document is
  stored in an <<glossary-index,index>> and has a type
  and an <<glossary-id,id>>.
  
  A document is a JSON object (also known in other languages as a hash /
  