class_docstr: Reduce corpus to the X most important terms.  Great for plotting a big corpus.
  Will return between X/2 and X terms.
  
  Returns the terms with the X highest absolute scores, background corpus scores, and term frequencies.
code: def _add_default_num_terms_to_keep(num_term_to_keep):
      if num_term_to_keep is None:
          num_term_to_keep = 4000
      return num_term_to_keep
  
label_desc: Use image node_id 6 for calling the AutoTermSelector obj's underlying member method code with example usage: obj._add_default_num_terms_to_keep(num_term_to_keep) and returns: num_term_to_keep