IHelpSystem allows an application to do three things:

• Provides path information to the Help Manager.
• Provides a new Help selector.
• Asks the Help Manager to display Help.

Providing path information is important because the Help Manager is platform-independent and Help system-independent and so is not able to ascertain the location of Help files. If an application expects Help to be provided by an external Help system that is not able to ascertain file locations itself, it must provide this information through the IHelpSystem's ProvideHelpPath method, which allows the information to become available through the IHelpManager's GetHelpPath method. (This information propagates outward only if the Help viewer asks for it.) 

Assigning a Help selector allows the Help Manager to delegate decision-making in cases where multiple external Help systems can provide Help for the same keyword. For more information, see the topic Implementing IHelpSelector. 

IHelpSystem exports four procedures and one function to request the Help Manager to display Help:

• ShowHelp
• ShowContextHelp
• ShowTopicHelp
• ShowTableOfContents
• Hook

Hook is intended entirely for WinHelp compatibility; it allows processing of WM_HELP messages that cannot be mapped directly onto requests for keyword-based, context-based, or topic-based Help. The other methods each take two arguments: the keyword, context ID, or topic for which help is being requested, and the Help file in which it is expected that help can be found. 

In general, unless you are asking for topic-based help, it is equally effective and more clear to pass help requests to the Help Manager through the InvokeHelp method of your control.