DeltaTick programming blocks - a collection of blocks that typically reflect mid-grained behaviors appropriate for a specific content area (such as population dynamics, or natural selection) - are loaded from fully editable and authorable XML "Behavior Libraries". They can also be loaded in combination with any number of other libraries.
DeltaTick is still under development. It is currently used along with HotLink Replay, a new analysis interface for NetLogo, to study students' understanding of the Mathematics of Change in Complex Systems.
You can learn more about DeltaTick, HotLink, and our studies at the Center for Connected Learning's website, or on the CCL's papers page.