What is the length and characters in identifiers created by elasticsearch?

Question

elastic search state documentation :

An index operation can be performed without specifying an identifier. In this case, the identifier will be generated automatically.

But it does not provide any information about the properties of identifiers.

• What is the length (minimum / maximum)? My hunch 22.
• What characters are used in the identifier?
  My hunch[-_A-Za-z0-9]
• Can the properties of the generated identifiers change at any time (this is part of the API)?

Answer 1

base64 -encoded UUID. base64 , URL, - _ .

Answer 2

elasticsearch 20 ( 22 ) url- base64 [-_A-Za-z0-9].

: https://www.elastic.co/guide/en/elasticsearch/guide/master/index-doc.html#_autogenerating_ids