My answer was too terse. IF there was two :: in the address, then the length of EACH :: denoted section is not known. It can be either longest left :: or longes

My answer was too terse. IF there was two :: in the address, then the length of EACH :: denoted section is not known. It can be either longest left :: or longest right :: and that wasn't defined, because the rule is THERE IS ONLY ONE :: section. Posed as a question, disingenuously.