docs: def replace_baseline_repr(self, linenum, update):
          """Replace individual baseline representation.
  
          :param int linenum: location of baseline representation
          :param str update: new baseline representation text (with delimiters)
  
          """
          # use property to access lines to read them from file if necessary
          lines = self.lines
  
          count = 0
          delimiter = None
          for index in range(linenum - 1, -1, -1):
              line = lines[index]
              if delimiter is None:
                  single_quote_index = line.rfind("'''")
                  double_quote_index = line.rfind('"""')
                  if double_quote_index >= 0:
                      if double_quote_index > single_quote_index:
                          delimiter = '"""'
                      else:
                          delimiter = "'''"
                  elif single_quote_index >= 0:
                      delimiter = "'''"
                  else:
                      continue
              count += lines[index].count(delimiter)
              if count >= 2:
                  linenum = index
                  break
          else:
              docstr_not_found = (
                  '{}:{}: could not find baseline docstring'
                  ''.format(self.showpath(self.path), linenum))
              raise RuntimeError(docstr_not_found)
  
          old_content = '\n'.join(lines[linenum:])
  
          match = self.REGEX.match(old_content)
  
          if match is None:
              docstr_not_found = (
                  '{}:{}: could not find docstring'.format(self.path, linenum))
              raise RuntimeError(docstr_not_found)
  
          new_content = match.group('prefix') + update + match.group('suffix')
  
          lines[linenum:] = new_content.split('\n')