BaseWindow defines an interface for types that represent a Windows window.
It requires implementors to provide a method to retrieve the window's handle (HWND)
along with an error status to indicate success or failure.
Flag represents a bit field used to specify options or attributes in Windows API calls.
It is typically used to configure behavior or properties, such as those in message boxes or windows.
Style represents a bit field used to define the visual or behavioral style of a Windows window.
It is commonly used in window creation or modification to set characteristics like borders or visibility.