src/core/Registry.php
public function set(string $key, $value): self
    {
        $this->store[$key] = $value;
        return self::$instance;
    }
public function set(string $key, $value): self
    {
        $this->store[$key] = $value;
        return self::$instance;
    }
It adds the user variable to the storage.
@param string $key The variable name.
@param mixed $value The variable value.
@return self.