# Open Discussion: Modifier Areas

*These are collaborative notes from the open discussion round about "Modifier Areas" at the [Solidity Summit 2020](https://solidity-summit.ethereum.org/).*

Possible use cases:
- Re-entrancy guard/mutex.
- This won't work.
- Precondition, postcondition, invariant.
- Clearly distinguishing an area of dangerous, admin-only functions.
- A quick and dirty way to profile the gas usage of a function for testing.

Modifiers can't easily be reused between libraries and regular contracts.