Adding file types to document classes in NetBeans

NetBeans handles nearly all file types and colour codes it all very nicely. However it doesn't recognise Smarty template files (.tpl) and finding where I can add .tpl files to NetBeans always baffles me.

Tools >> Options >> Miscellaneous >> Files

Then click 'New' next to the 'File Extension' dropdown and enter 'tpl'. Associating it with the HTML file type worked better for me than PHP.