You cannot quote a line to avoid a boundary clash. You have to pick a
marker that does not appear. In practice this is not a problem to do.
You can scan the message if you want to be 100% sure, but use of
relatively simple algorithms will generate a line for you that will
clash with arbitrarily low probability. I chose an approach that will
generate a conflict about one time in 1E38. If you look at the reliability
of the checksums on a typical network, you'll find that 1E38 might as
well be zero -- you'll lose a boundary marker to a network erro more
often than you'll gain one from a false match.
Ned