SF bug #719367, string exceptions are deprecated
Remove references to string based exceptions in the doc.
diff --git a/Doc/ref/ref4.tex b/Doc/ref/ref4.tex
index 0eb6841..b993266 100644
--- a/Doc/ref/ref4.tex
+++ b/Doc/ref/ref4.tex
@@ -183,12 +183,9 @@
\exception{SystemExit}\withsubitem{(built-in
exception)}{\ttindex{SystemExit}}.
-Exceptions are identified by string objects or class instances.
-Selection of a matching except clause is based on object identity
-(i.e., two different string objects with the same value represent
-different exceptions!) For string exceptions, the \keyword{except}
-clause must reference the same string object. For class exceptions,
-the \keyword{except} clause must reference the same class or a base
+Exceptions are identified by class instances.
+Selection of a matching except clause is based on object identity.
+The \keyword{except} clause must reference the same class or a base
class of it.
When an exception is raised, an object (maybe \code{None}) is passed