What does “advanced properties” mean in an error message in a .eslintrc file?

Question

I am making an .eslintrc file that contains the "indent" rule. The configuration for the rule is as follows:

"indent": ["error", 2, { ..., "FunctionDeclaration": {"parameters": 2, "body": 1}, "FunctionExpression": {"parameters": 2, "body": 1}, }] 

However, when running eslint, I get an error message:

 Configuration for rule "indent" is invalid: Value "data["1"].FunctionDeclaration" has additional properties. Value "data["1"].FunctionExpression" has additional properties. 

What does this error message mean? I would suggest that this means that either (a) there are more properties that are mandatory for FunctionDeclaration that are not there, or (b) one of the properties ("parameters" or "body") that are in the function declaration is not should be there. I think I can exclude (b), because when I change the .eslintrc file to:

  "indent": ["error", 2, { ..., "FunctionDeclaration": {}, "FunctionExpression": {}, }] 

I get the same error message although there are no properties. And all the documentation that I could find says that the only necessary properties are "parameters" and "body", I could not find anything that indicates the presence of the necessary properties, except for this. What is the problem?