public function getRegions($type = null)
    {
        if (null === $type) {
            return array_keys($this->matrix);
        }

        $regions = [];
        foreach ($this->matrix as $region => $types) {
            if (in_array($type, $types)) {
                $regions[] = $region;
            }
        }

        return $regions;
    }
public function getRegions($type = null)
    {
        if (null === $type) {
            return array_keys($this->matrix);
        }

        $regions = [];
        foreach ($this->matrix as $region => $types) {
            if (in_array($type, $types)) {
                $regions[] = $region;
            }
        }

        return $regions;
    }
Returns the available regions for a specified type.
If not specified, all regions are returned.

@param null $type

@return array