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§27.3. Built-in, installed and project-specific extensions

To recap: Inform builds projects from both the source text typed by the author and from Extensions; one of these, the Standard Rules, is always included; others are added as authors please. About 20 are "built-in" to Inform, meaning that they are stored inside the application and always available. Others must be "installed", and each Inform user will have a folder somewhere on his computer which contains these. Users typically obtain these from the Public Library feature in the Inform application, but can also download them directly from the extension writer's website and then use an Install Extension menu option in the application. Either way, the application then squirrels the file away, and it becomes available to any projects that that user may be working on.

It is also possible to have extensions available to just one project. These must be stored in the Extensions subfolder of the project's ".materials" folder, but otherwise are arranged the same as installed extensions - there's an outer folder for each author's name, and extensions are named with a ".i7x" extension within. For example:

Mourning Hypercritical.inform
Mourning Hypercritical.materials
    Extensions
        John Siracusa
            Fixing The Finder.i7x

When Inform needs to find an extension, it looks here first, then in the installed area, then in its built-in area. That means that we can make our own revised or hacked version of an extension, put it in the ".materials" area, and then have it take precedence over the installed or built-in one. We could even have our own private version of the Standard Rules here.

(This has a number of possible uses - for example, to provide a convenient test-bed when working on an experimental version of an extension.)


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