code: func (e *edit) ReplaceAtLineN(r []ReplacerAtLine, n int) error {
  	return e.genReplaceAtLine(r, n)
  }
docs: // ReplaceAtLine replaces regular expressions mathed in r, if the line is
  // matched at the first. The count determines the
  // number to match:
  //   n > 0: at most n matches
  //   n == 0: the result is none
  //   n < 0: all matches