The Help system allows communication between your application and Help viewers through a series of interfaces. These interfaces are all defined in the HelpIntfs.pas, which also contains the implementation of the Help Manager. 

ICustomHelpViewer provides support for displaying Help based upon a provided keyword and for displaying a table of contents listing all Help available in a particular viewer. 

IExtendedHelpViewer provides support for displaying Help based upon a numeric Help context and for displaying topics; in most Help systems, topics function as high-level keywords (for example, "IntToStr" might be a keyword in the Help system, but "String manipulation routines" could be the name of a topic). 

ISpecialWinHelpViewer provides support for responding to specialized WinHelp messages that an application running under Windows may receive and which are not easily generalizable. In general, only applications operating in the Windows environment need to implement this interface, and even then it is only required for applications that make extensive use of non-standard WinHelp messages. 

IHelpManager provides a mechanism for the Help viewer to communicate back to the application's Help Manager and request additional information. IHelpManager is obtained at the time the Help viewer registers itself. 

IHelpSystem provides a mechanism through which TApplication passes Help requests on to the Help system. TApplication obtains an instance of an object which implements both IHelpSystem and IHelpManager at application load time and exports that instance as a property; this allows other code within the application to file Help requests directly when appropriate. 

IHelpSelector provides a mechanism through which the Help system can invoke the user interface to ask which Help viewer should be used in cases where more than one viewer is capable of handling a Help request, and to display a Table of Contents. This display capability is not built into the Help Manager directly to allow the Help Manager code to be identical regardless of which widget set or class library is in use.