# Objective
- All UI systems should be in system sets that are easy to order around
in user code.
## Solution
- Add `UiSystem::Prepare` and `UiSystem::PostLayout` system sets to
capture floater systems.
- Adjust how UI systems are scheduled to align with the new sets.
This is *mostly* a pure refactor without any behavior/scheduling
changes. See migration guide.
## Testing
- Not tested, correctness by inspection.
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## Migration Guide
`UiSystem` system set adjustments.
- The `UiSystem::Outline` system set is now strictly ordered after
`UiSystem::Layout`, rather than overlapping it.