Their rule does work. The single quotes are transformed into '\''. The first ' closes the current single quotes string. The \' adds a single quote character ou

Their rule does work. The single quotes are transformed into '\''. The first ' closes the current single quotes string. The \' adds a single quote character outside a quoted string (and outside single quotes you can use backslash escapes). Finally, the last ' reopens the single quoted string that we closed before.