How to do line- and message-delimination

I'm trying to write a NWProtocolFramerImplementation class that will be channeled through a Framer wrapper. There are still some parts I need figuring out.

• For handleOutput(framer: message: messageLength: isComplete), what do the last two parameters do? Does isComplete refer to the end of the current conversation, or the entire connection? Why would we submit a messageLength if the data size should already be implied within message?
• If I parse by line breaks, is there a way to indicate if the latest line is the last of the current conversation, either input or output?