UserCallback

This event allows the calling process to insert optional data into selected points of the HTML output. This event is triggered by the inclusion of the $USERCB=X token in one of the properties, where X identifies the callback. The text in szUserString is inserted in the HTML. See $USERCB.

UserCallback([in] BSTR szUserString,
             [out, retval] BSTR *pszVal);

The compsamp sample program demonstrates how to use this event.