lib/Elastica/QueryBuilder/DSL/Query.php
public function regexp(string $key = '', string $value = null, float $boost = 1.0): Regexp
    {
        return new Regexp($key, $value, $boost);
    }
public function regexp(string $key = '', string $value = null, float $boost = 1.0): Regexp
    {
        return new Regexp($key, $value, $boost);
    }
public function regexp ( string $ key = '' , string $ value = null , float $ boost = 1.0 ) : Regexp { return new Regexp ( $ key , $ value , $ boost ) ; }
regexp query.

@param string $key
@param string $value
@param float  $boost

@return Regexp

@see https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-regexp-query.html
regexp query .