Without contract / with contract in components

1) Masters 1.0 (Now deprecated)

• No controllers

2) Components without contract

• Always has controller
• Instances always show complete widget hierarchy as in source
• No custom events
• All properties can be overwritten in instance

3) Components with contract

• Always has controller
• Instance doesn't show any hierarchy (unless explicitly exposed)
• Custom events
• Control over what properties can be overwritten in instance (by making them pass-through)

So if you want to build you own calculator component and expose selected custom events for any user, you should choose components with contract.