domain name labels are limited to 63 characters

You probably now that labels in domain names are limited to 63 characters
and the whole domain name is limited to 255 characters.

The specification says that if after expanding the macros a <domain-spec> is
longer than 255, then the SPF implementation must remove labels on the left
side until the length is not longer than 255.

But the specification does not say what to do if after expanding the macros
a domain name label is longer than 63 characters. (This may happen for
example if the local-part has no dot and is 64 characters long and
<domain-spec> contains the "%{l}" macro).

If that case, should the SPF inplementation return PermFail?

Or should it truncate the label to 63 characters? If yes, on the left or on
the right side?

Or should it split the label into multi labels, that means insert dots?

Roger