src/ArrayObject.php
protected function getNormalizedKey($key): string
    {
        // Keys within collections must be offset based
        if (!\is_int($key) && $this->isCollection() && !preg_match('/^\d+\./', $key)) {
            $key = "0.$key";
        }

        return $key;
    }
protected function getNormalizedKey($key): string
    {
        // Keys within collections must be offset based
        if (!\is_int($key) && $this->isCollection() && !preg_match('/^\d+\./', $key)) {
            $key = "0.$key";
        }

        return $key;
    }
protected function getNormalizedKey ( $ key ) : string { // Keys within collections must be offset based if ( ! \ is_int ( $ key ) && $ this -> isCollection ( ) && ! preg_match ( '/^\d+\./' , $ key ) ) { $ key = "0.$key" ; } return $ key ; }
Forces key to be prefixed with an offset.

@param $key

@return string
Forces key to be prefixed with an offset .