yii\mongodb\QueryBuilder::buildRegexCondition PHP Method

    public function buildRegexCondition($operator, $operands)
    {
        if (!isset($operands[0], $operands[1])) {
            throw new InvalidParamException("Operator '{$operator}' requires two operands.");
        }
        list($column, $value) = $operands;
        if (!$value instanceof Regex) {
            if (preg_match('~\\/(.+)\\/(.*)~', $value, $matches)) {
                $value = new Regex($matches[1], $matches[2]);
            } else {
                $value = new Regex($value, '');
            }
        }
        return [$column => $value];
    }