The regex query allows you to use regular expressions to match terms in the _all field.
A detailed overview of lucene's regex engine is available here: <a target=“_blank” href=“Regular”>www.elasticsearch.org/guide/en/elasticsearch/reference/current/query-dsl-regexp-query.html#regexp-syntax“>Regular expressions in Elasticsearch</a>
<h5>A note on anchoring</h5> Lucene’s patterns are always anchored. The pattern provided must match the entire string. For string “abcde”: <p> ab.*
will match
abcd
will not match</br>