The Law of One Form

In the Burton Watson translation of the Lotus Sutra, on page 136-7 there is mentioning of "The law of one form" Here is an exerpt of where this is mentioned by Shakyamuni: > "The thus come one knows that this is the law of one form, one flavor, namely, the form of emancipation, the form of ultimate nirvana, of constant tranquility and extinction, which in the end finds its destination in emptiness. The Buddha understands all this." Is there another name for the law of one form, because when I looked it up on the internet, -but perhaps my searching skills aren't very good- I couldn't find much anything about it and I would like to learn more.