UX Core — MRTK3
This package includes the core scripts and behaviors for building custom UI controls from scratch. For developers intending to build their own custom component libraries, this package should be the only necessary dependency and won't include any pre-built prefabs.
On the other hand, most developers will likely only need the pre-built UX components. If you're looking for pre-built UX controls, the UX Components package includes our libraries of ready-to-use UX prefabs. The Components package includes this core package as a dependency.