In both models, you use a C or Pascal compiler to create a code resource, and then copy the code resource into Frontier's object database. Once the code is in the database, your scripts can call them, send parameters, and receive returned values, just as if they were verbs built into the UserTalk language. XCMDs are HyperCard 1.0-compatible code extensions. UCMDs are compiled Apple Event handlers. Each approach has advantages.
Hierarchic lists come up all the time when designing software.
Until outline sharing there was no standard way for applications to easily communicate and manage large hierarchic structures. The Outline Sharing Toolkit also suggests how to approach toolkits for other data types that can be transported using the Apple Events protocol. OutlineSharer is the sample application for outline sharing. UserLand's Bullet application, a color outline browser, builds on the Outline Sharing Toolkit. It's available as a separate download.