diff --git a/Shortcut-handling.md b/Shortcut-handling.md
index 8044328..7da256e 100644
--- a/Shortcut-handling.md
+++ b/Shortcut-handling.md
@@ -1,7 +1,14 @@
 ### Format
 
-    bindsym [--release] [--locked] <Modifiers><Keysyms> <command>
-    bindcode [--release] [--locked] <Modifiers><Keycodes> <command>
+    bindsym [--release] [--locked] [<Modifiers>+]<Keysyms> <command>
+    bindcode [--release] [--locked] [<Modifiers>+]<Keycodes> <command>
+
+`<Modifiers>` is a (possibly empty) `+` separated list of modifier bit flag names.
+(`Shift`=`0x01`, `Lock`=`0x02`, `Ctrl`=`0x04`,  `Mod1`=`Alt`=`0x08`, `Mod2`=`0x10`, `Mod3`=`0x20`, `Mod4`=`0x40`, `Mod5`=`0x80`). These names should not be confused with the keys whose
+pressing might produce the modifier; on US keyboards, keysym `Alt_L` (keycode 64) and keysym `Alt_R` (keycode 108) both produce the `Alt` modifier.
+
+
+The binding specifications here mostly overlap with those from i3 (see https://i3wm.org/docs/userguide.html#keybindings).
 
 ### How to identify keys