Builtins.md

@@ -22,6 +22,14 @@ println(my_str + "world!"); // prints "Hello world!"
 
 Use a plus sign like Python or Java!
 
+### String Length
+
+```
+#"hello world!" // expression results in 11
+```
+
+Basically Lua: use the number sign on a string.
+
 ### Substring
 
 ```