class_docstr: A mention (possible anaphor) inherite from spacy Span class with additional informations
docstr: Returns an iterator of nouns/proper nouns in the Mention 
docstr_tok: ["Returns","an","iterator","of","nouns\/proper","nouns","in","the","Mention"]
code: def content_words(self):
      """Returns an iterator of nouns/proper nouns in the Mention"""
      return (tok.lower_ for tok in self if tok.tag_ in PROPERS_TAGS)
  
imports: import re
  import io
  from six import string_types, integer_types
  from spacy.tokens import Span, Token
  from neuralcoref.train.compat import unicode_
  from neuralcoref.train.utils import encode_distance, parallel_process
  import spacy
  import numpy
label_desc: Use image node_id 7 for calling the Mention obj's underlying member method code with example usage: obj.content_words() and returns: unknown