Anything the user decides to put in the refrigerator, provided we put warnings in small text on the document that accompanies the refrigerator for catogories of items we know to be unfit for the refrigerator so as to cover our asses if the user does not heed our warnings.<p>In terms of software, trying to decide up front for the user what they can do is the wrong approach. Even constraining them is flawed, with the exception of constraints for liability issues. What the user needs is the meas to express their decision making as to whether something should go into the fridge, so they need an input mechanism capable of doing selection, which has access to the context in which the item might be being placed into the fridge.<p>Does this sound like any configuration format you&#x27;ve ever used? The typical key-value stores which attempt to give you a declarative list of what you can put where, without the means to compute whether or not it might be a good idea first are almost ubiquitous, and the number of programs which take the right approach: give the user a proper, expressive programming language to configure the software, are few.<p>Just as it happens, we&#x27;ve developed ACME Refrigerator v2.0, which now allows you to store chocolate bars in it; a feature we missed in v1.0. Upgrade now for just $400.<p>The absurity of this idea with a fridge seems lost in software because we can upgrade at almost zero cost in just a few minutes, but that&#x27;s only masking what is an obvious design flaw.<p>Which raises the question: What can you put in a software package definition?