You need to install the Inform Attack extension (so Inform can potentially use it) and include into your project (so Inform knows that it should actually use it in that project).
To install it: Open up Inform. Choose “Install Extension” from the File Menu and … well … install it.
To include it: Just add the line “Include Inform Attack by Victor Gijsbers.” at the top of your source text.
(In the IDE, you can see a list of all your installed extensions by clicking the text “Installed Extensions” under the chapter headings to built-in Documentation.)
