file/edit.go
func (e *edit) ReplaceAtLineN(r []ReplacerAtLine, n int) error {
	return e.genReplaceAtLine(r, n)
}
func (e *edit) ReplaceAtLineN(r []ReplacerAtLine, n int) error {
	return e.genReplaceAtLine(r, n)
}
// 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