[geckoday]

Smarty 2 doc is found in the same place as the Smarty 3 doc. smarty.net, click on documentation in the menu bar and it lists smarty 2 doc links just below the smarty 3 doc links. But as Steve noted that won't help you as interline isn't part of smarty, its a custom function so you'll need to look at the code to see what it does.