Tracking: IBoundary<T> API

## Definition
````C#
public interface IBoundary<T>
{
    T Value { get; }
    BoundaryType { get; }
    bool IsValid { get; }
    internal void ThisInterfaceCannotBeImplemented()
}
````

## Implementation
- [x] Done.

## XML documentation
- [ ] Done.

## Proper documentation
- [ ] Done.