class_docstr: Result summary
  
  Construction does not take any parameters. Tables and text can be added
  with the `add_` methods.
  
  Attributes
  ----------
  tables : list of tables
      Contains the list of SimpleTable instances, horizontally concatenated
      tables are not saved separately.
  extra_txt : str
      extra lines that are added to the text output, used for warnings
      and explanations.
docstr: add additional text that will be added at the end in text format
  
  Parameters
  ----------
  etext : list[str]
      string with lines that are added to the text output.
docstr_tok: ["add","additional","text","that","will","be","added","at","the","end","in","text","format","Parameters","--","--","--","--","--","etext",":","list","[","str","]","string","with","lines","that","are","added","to","the","text","output","."]
code: def add_extra_txt(self, etext):
      """add additional text that will be added at the end in text format
  
      Parameters
      ----------
      etext : list[str]
          string with lines that are added to the text output.
  
      """
      self.extra_txt = "\n".join(etext)
  
imports: from statsmodels.compat.python import lmap, lrange, lzip
  import copy
  from itertools import zip_longest
  import time
  import numpy
  from statsmodels.iolib.table import SimpleTable
  from statsmodels.iolib.tableformatting import fmt_2, fmt_2cols, fmt_params, gen_fmt
  from .summary2 import _model_types
label_desc: Use image node_id 8 for calling the Summary obj's underlying member method code with example usage: obj.add_extra_txt(etext) without return types