code: def find_start_of_previous_word(self, count=1, WORD=False):
          
          # Reverse the text before the cursor, in order to do an efficient
          # backwards search.
          text_before_cursor = self.text_before_cursor[::-1]
  
          regex = _FIND_BIG_WORD_RE if WORD else _FIND_WORD_RE
          iterator = regex.finditer(text_before_cursor)
  
          try:
              for i, match in enumerate(iterator):
                  if i + 1 == count:
                      return - match.end(1)
          except StopIteration:
              pass
docs: Return an index relative to the cursor position pointing to the start
          of the previous word. Return `None` if nothing was found.