code: def from_chain(cls, chain_json, corpus=None, parsed_sentences=None):
          
          chain = Chain.from_json(chain_json)
          return cls(corpus or None, parsed_sentences=parsed_sentences, state_size=chain.state_size, chain=chain)
docs: Init a Text class based on an existing chain JSON string or object
          If corpus is None, overlap checking won't work.