Names Default To Here( 1 );
The Names Default To Here( 1 ); function makes all unscoped variables in the script local to that script and does not affect the global variable namespace. Advanced Scoping and Namespaces provides more details.
Note: The Names Default to Here option is true by default for custom menus and toolbar buttons. A script that runs when you select a custom menu item or click a custom toolbar button does not affect global variables.