* memw usage more clear

docs/user.tex

@@ -1318,7 +1318,7 @@ match exactly. The reason for this is the function overloading mechanism of
 \item \var {(* ... *)} as comment delimiters are not allowed in versions
 older than 0.9.1. This can easily be remedied with a grown-up editor. 
 \item The \var{MEM, MEMW, MEML} and \var{PORT} variables for memory and port
-access are not available. This is due to the operating system. Under
+access are not available in the system unit. This is due to the operating system. Under
 \dos, the extender unit (\file {GO32.PPU}) implements the mem constuct.
 under \linux, the \file{ports} unit implements such a construct.
 \item \var{PROTECTED, PUBLIC, PUBLISHED, TRY, FINALLY, EXCEPT, RAISE}