elasticsearch/docs/reference/scripting-languages/painless/painless-identifiers.md

mapped_pages	products
https://www.elastic.co/guide/en/elasticsearch/painless/current/painless-identifiers.html	id painless

Identifiers [painless-identifiers]

Use an identifier as a named token to specify a variable, type, field, method, or function.

Errors

If a keyword is used as an identifier.

Grammar

ID: [_a-zA-Z] [_a-zA-Z-0-9]*;

Examples

• Variations of identifiers.

  a
  Z
  id
  list
  list0
  MAP25
  _map25
  Map_25