This setting specifies an identifier for the first topic to display. This is a JavaHelp-specific target name rather than a file name. Typically it is the ObjectID of the first heading in the file; for example, Xaa123456. The default-topic identifier appears in a helpset file entry such as the following:
If you do not specify a value for DefaultTopic, Mif2Go tries to autodetect the target name; however, this works only if Mif2Go is rewriting the helpset file after the first time you ran the conversion. Mif2Go uses the first topic ID in the first file in the book. If all else fails, Mif2Go uses the base name of the FrameMaker book (or single FrameMaker file).