multipart messages, the body is a table that
recursively defines each part as an independent message, plus an optional
<tt>preamble</tt> and <tt>epilogue</tt>.
</p>

<p class=return> 
The function returns a <em>simple</em> 
<a href="http://lua-users.org/wiki/FiltersSourcesAndSinks">LTN12</a> 
source that produces the
message contents as defined by <tt>mesgt</tt>, chunk by chunk. 
Hopefully, the following
example will make things clear. When in doubt, refer to the appropriate RFC
as listed in the introductio