Sat Apr 15 10:23:09 EDT 2017

What is a message?

It's a goto. It's a single-ended continuation invocation. This is the
original idea behind Scheme.

In Forth it isn't much different from other languages.

The main point is that "large" messages should be encoded in a way
that allows them to be routed without being buffered.

What is a large message?  It either contains a certain grouping of
commands for one or more nodes, or it contains payload data that is to
be delivered to some port.