FilterOut removes all errors that match any of the matchers from the input error.

Flatten takes an Aggregate, which may hold other Aggregates in arbitrary nesting, and flattens them all into a single Aggregate, recursively.

NewAggregate converts a slice of errors into an Aggregate interface, which is itself an implementation of the error interface.

Aggregate represents an object that contains multiple errors, but does not necessarily have singular semantic meaning.

Matcher is used to match errors.