class_docstr: Object for core-components (POS, Dependency Relations, etc).
  
  Attributes:
      _doc_text: the doc text
      _sentences: list of sentences, each word in a sentence is
          represented by a dictionary, structured as follows: {'start': (int), 'len': (int),
          'pos': (str), 'ner': (str), 'lemma': (str), 'gov': (int), 'rel': (str)}
code: def sent_text(self, i):
      parsed_sent = self.sentences[i]
      first_tok, last_tok = parsed_sent[0], parsed_sent[-1]
      return self.doc_text[
          first_tok["start"] : last_tok["start"] + last_tok["len"]
      ]
  
imports: import json
  from nlp_architect.utils.io import validate
label_desc: Use image node_id 13 for calling the CoreNLPDoc obj's underlying member method code with example usage: obj.sent_text(i) and returns: self