In section 2.2, change
IN NAPTR 100 10 "U" "Meta:CPPA" "Unable to render embedded object: File (//example.com/cppa) not found."
to
IN NAPTR 100 10 "U" "Meta:CPPA" "Unable to render embedded object: File (//example.com/cppa) not found."
and change
IN NAPTR 100 10 "U" "Meta:SMP" "Unable to render embedded object: File (//example.com/smp) not found."
to
IN NAPTR 100 10 "U" "Meta:SMP" "Unable to render embedded object: File (//example.com/smp) not found."
In 2.3.2, change
IN NAPTR 100 10 "U" "Meta:SMP" "Unable to render embedded object: File (//serviceprovider.peppol.eu/e49b223851f6e97cbfce4f72c3402aac/) not found."
to
IN NAPTR 100 10 "U" "Meta:SMP" "Unable to render embedded object: File (//serviceprovider.peppol.eu/e49b223851f6e97cbfce4f72c3402aac/) not found."
The example using group extraction can stay as it is, as it already mentions that implementations should beware of varying server-side implementations of regexp backslash escaping.