Add HIDDEN. Fixes #777664.
diff --git a/Lib/lib-tk/Tkconstants.py b/Lib/lib-tk/Tkconstants.py
index 2686877..ac57952 100644
--- a/Lib/lib-tk/Tkconstants.py
+++ b/Lib/lib-tk/Tkconstants.py
@@ -70,6 +70,8 @@
 NORMAL='normal'
 DISABLED='disabled'
 ACTIVE='active'
+# Canvas state
+HIDDEN='hidden'
 
 # Menu item types
 CASCADE='cascade'