tabs, newlines and crs are valid XML characters.

Doc/lib/libxmlrpclib.tex

@@ -94,7 +94,8 @@ When passing strings, characters special to XML such as \samp{<},
 \samp{>}, and \samp{\&} will be automatically escaped.  However, it's
 the caller's responsibility to ensure that the string is free of
 characters that aren't allowed in XML, such as the control characters
-with ASCII values between 0 and 31; failing to do this will result in
+with ASCII values between 0 and 31 (except, of course, tab, newline and
+carriage return); failing to do this will result in
 an XML-RPC request that isn't well-formed XML.  If you have to pass
 arbitrary strings via XML-RPC, use the \class{Binary} wrapper class
 described below.