public function addGlobalSubstitutions($substitutions)
    {
        if (current($substitutions) instanceof Substitution) {
            foreach ($substitutions as $substitution) {
                $this->addGlobalSubstitution($substitution);
            }
        } else {
            foreach ($substitutions as $key => $value) {
                $this->addGlobalSubstitution($key, $value);
            }
        }
    }