class_docstr: object for annotation documents
  
  Args:
      self.doc_text (str): document text
      self.annotation_set (list(str)): list of all annotations in doc
      self.spans (list(dict)): list of span dict, each span_dict is structured as follows:
          { 'end': (int), 'start': (int), 'type': (str) string of annotation }
docstr: Return doc adapted to displacyENT expected input
docstr_tok: ["Return","doc","adapted","to","displacyENT","expected","input"]
code: def displacy_doc(self):  # only change annotations to lowercase
      """
      Return doc adapted to displacyENT expected input
      """
      self.annotation_set = [
          annotation.lower() for annotation in self.annotation_set
      ]
      return self.__dict__
  
imports: from __future__ import unicode_literals, print_function, division, absolute_import
  import json
label_desc: Use image node_id 4 for calling the HighLevelDoc obj's underlying member method code with example usage: obj.displacy_doc() and returns: self