Update runtime files
diff --git a/runtime/doc/vi_diff.txt b/runtime/doc/vi_diff.txt
index 82f6274..f762e8a 100644
--- a/runtime/doc/vi_diff.txt
+++ b/runtime/doc/vi_diff.txt
@@ -1,4 +1,4 @@
-*vi_diff.txt* For Vim version 8.1. Last change: 2019 Oct 12
+*vi_diff.txt* For Vim version 8.1. Last change: 2019 Nov 12
VIM REFERENCE MANUAL by Bram Moolenaar
@@ -1323,6 +1323,11 @@
flags when Vim starts up. This makes Vim run as POSIX as it can. That's
a bit different from being Vi compatible.
+You can find the Posix specification for Vi here:
+https://pubs.opengroup.org/onlinepubs/9699919799/utilities/vi.html
+And the related Ex specification:
+https://pubs.opengroup.org/onlinepubs/9699919799/utilities/ex.html
+
This is where Vim does not behave as POSIX specifies and why:
*posix-screen-size*