document non-BSD SIGCHLD behaviour
diff --git a/Doc/lib/libsignal.tex b/Doc/lib/libsignal.tex
index 63b671f..802c4d1 100644
--- a/Doc/lib/libsignal.tex
+++ b/Doc/lib/libsignal.tex
@@ -8,7 +8,10 @@
\item
A handler for a particular signal, once set, remains installed until
-it is explicitly reset (i.e. Python uses the BSD style interface).
+it is explicitly reset (i.e. Python emulates the BSD style interface
+regardless of the underlying implementation), with the exception of
+the handler for \code{SIGCHLD}, which follows the underlying
+implementation.
\item
There is no way to ``block'' signals temporarily from critical