Using libraries
Libraries allow you to reuse elements in multiple games. That might be object types, functions, or even common objects. In fact, libraries are the basis of how Quest works - Core.aslx is a library, included by default in all Quest games. It handles much of the standard text adventure game functionality - working out which objects the player can see, handling player commands, implementing containers, and much more. This means that Quest's built-in functionality is extensible and indeed replaceable.
If you've created some functionality in your game that you think would be useful to others, consider turning it into a library. See Creating Libraries for more information.
You can download libraries from the Resources page. When you've downloaded a library, go to Included Libraries in the tree (under the Advanced section) and click Add to add it to your game.