Rule definition and structure

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 the changes in the update or write.
newData	It represents the Data Snapshot before applying the given database operation. However, it includes both the existing data as well as the new data, which includes data manipulated by the given data operation.
now	It represents current...