Problem
Slots are a powerful way to make components flexible, but today they are too open. Even when using Preferred Instances, designers can still insert any component or element into a slot. This flexibility often leads to misuse and breaks design system consistency—especially in large teams.
Example:
A Button component has an Icon slot.
We want designers to use only approved icon components, but currently they can insert:
- Any other component
- Any vector or frame
- Any custom element
This results in inconsistent UI, broken behavior, and extra review overhead for design system teams.
Proposed Feature
Add an option to restrict slot content to specific components or component sets.
When creating or editing a slot, allow authors to:
- Define a restricted list of allowed components / component sets
- Prevent adding any elements outside this list
- Optionally show an error or warning when invalid content is attempted
How this differs from Preferred Instances
- Preferred Instances → Suggests what should be used
- Restricted Instances (proposed) → Enforces what can be used
This distinction is critical for maintaining design system integrity at scale.
Benefits
- Stronger design system governance
- Fewer accidental violations
- Faster reviews and fewer fixes
- Better experience for non‑system‑expert designers
- More confidence when shipping reusable components
Use Cases
- Icon slots (icons only from an approved icon set)
- Media slots (only image or video components)
- Navigation items (only specific list item components)
- Enterprise design systems with strict standards
Summary
Adding restricted instance usage inside slots would bring much‑needed guardrails without reducing modularity. It would complement Preferred Instances perfectly and significantly improve consistency and scalability for design systems.
