Indicate that os.environ may not be a real dictionary.
diff --git a/Doc/lib/libposix.tex b/Doc/lib/libposix.tex
index 45f74af..e5108db 100644
--- a/Doc/lib/libposix.tex
+++ b/Doc/lib/libposix.tex
@@ -35,8 +35,8 @@
Module \module{posix} defines the following data items:
\begin{datadesc}{environ}
-A dictionary representing the string environment at the time
-the interpreter was started.
+A dictionary or dictionary look-alike representing the string
+environment at the time the interpreter was started.
For example,
\code{posix.environ['HOME']}
is the pathname of your home directory, equivalent to