diff --git a/examples/variables/variables.sh b/examples/variables/variables.sh
index 6513b1d..eb3b20d 100644
--- a/examples/variables/variables.sh
+++ b/examples/variables/variables.sh
@@ -4,3 +4,9 @@ initial
 true
 0
 apple
+
+# The shorthand `:=` initialization of variable can 
+# only be used inside any function.
+# If used outside any function, it would generate 
+# `syntax error: non-declaration statement outside 
+# function body`.