Functionality of "template" field on templates?

[Caladbolgll (Edmond)]

When setting up the basic beats system, there are default templates given in the package named as ___beat.template.json or ___beat.template-es6x.json (which apparently seem to be identical) (fill ___ with one of the beat's name). When I look at them, all of them end with a "template" parameter:

"template": "___beat-*"

When I search them, they just appear as one of the top-level field of the template (url obfuscated for confidentiality):

curl https://id:pw@some.elasticsearch.com:ppppp/_template?pretty=true
{
   ...
  "filebeat_test": {
    "order": 0,
    "template": "filebeat-*",
    ...
  }
}

I'd like to know what this "template" field is used for, since it neither defines the name of the template nor seems to work as an index.

[ruflin]

This should solve your questions: https://www.elastic.co/guide/en/elasticsearch/reference/5.6/indices-templates.html

Be aware that the setting was renamed in ES 6 to index_patterns.