Firebase rules provide predefined variables that can be used inside a rule definition:
| Name | Definition / Usage |
| auth | It represents information of the authenticated user. It will be null for an unauthenticated user. It is an object that contains uid, token, and provider fields and corresponding values. |
| $ variables | It represents wildcard path to refer to the dynamically generated keys and represent IDs. |
| root | It represents data snapshot at the root path in the Firebase database before applying the given database operation. |
| data | It represents the Data Snapshot before applying the given database operation. For example, in case of the update or write, the root represents the original data snapshot without ... |
