Please describe what the rule should do:
What category of rule is this? (place an "X" next to just one item)
[ ] Enforces code style [ ] Warns about a potential error [ ] Suggests an alternate way of doing something [ ] Other (please specify:)
Provide 2-3 code examples that this rule will warn about:
<!-- put your code examples here -->Why should this rule be included in ESLint (instead of a plugin)?