ICustomHelpViewer provides two methods relating to displaying tables of contents:

• CanShowTableOfContents
• ShowTableOfContents

The theory behind their operation is similar to the operation of the keyword Help request functions: the Help Manager first queries all Help viewers by calling ICustomHelpViewer.CanShowTableOfContents : Boolean and then invokes a particular Help viewer by calling ICustomHelpViewer.ShowTableOfContents. 

It is reasonable for a particular viewer to refuse to allow requests to support a table of contents. The Man page viewer does this, for example, because the concept of a table of contents does not map well to the way Man pages work; the HyperHelp viewer supports a table of contents, on the other hand, by passing the request to display a table of contents directly to WinHelp on Windows and HyperHelp on Linux. It is not reasonable, however, for an implementation of ICustomHelpViewer to respond to queries through CanShowTableOfContents with the answer True, and then ignore requests through ShowTableOfContents.