object decoder should have an option to throw error if extra properties are present

If an object is run through the decoder at runtime, there should be a way to configure the decoder to throw an error if the decoded object has extra properties not defined on the original decoder.

For example, given the following decoder:

interface MyType {
  myProperty?: string;
}

const MyTypeDecoder: Decoder<MyType> = object({
  myProperty: optional(string());
});

There should be an additional combinator to make the decoder throw an error given the following input:

const myTypeRuntimeValue: MyType = {
  myProperty: "someValue",
  myOtherProperty: "This one isn't defined on the interface"
};

// I want this to throw an error because myTypeRuntimeValue has
// an additional property not defined in the interface
const decoded = MyTypeDecoder.runWithException(myTypeRuntimeValue);

The combinator could be something like exact(value), e.g.

interface MyType {
  myProperty?: string;
}

const MyTypeDecoder: Decoder<MyType> = exact(object({
  myProperty: optional(string());
}));

Start by locating the object(), Decoder, optional(), string(), and runWithException entry points, then review existing decoder tests. Define how the proposed exact() combinator should treat undeclared properties and errors. Done means extra properties reliably cause decoding failure while declared and optional properties continue to work.