Time format for creating time-based indices

Where can I find the documentation on how to set my own date formats for time-based indices such as the default format of logstash-%{+YYYY.MM.dd}? I just want to know the proper syntax here. logstash-%{+xxxx.ww} is also mentioned as a variant in the elasticsearch output plugin docs ( https://www.elastic.co/guide/en/logstash/current/plugins-outputs-elasticsearch.html#plugins-outputs-elasticsearch-index ) for weekly log indices, but nothing else is mentioned.

Logstash uses JODA Time formatting. Use those letters.

This link is provided with the date filter documentation and also the sprintf documentation. It seems like we should explicitly link to the sprintf documentation in the Elasticsearch output documentation.

Thanks for the quick response!