The Input Source list box specifies the possible list of sources that
 will be scanned for dependencies when generating the description file.
 The OK button must be clicked for the list to be saved.

 Files are added to the list from the right-hand list box.  Files can be
 removed from the list by means of an arrow button (which is displayed when
 a file is highlighted).

 The top-most source specifies the source for the target of the complete
 build.  If a target is not specified in the MMS Description File Generator
 box, the top-most source name will be used for the target name.  A file can
 be moved up to the top of the list by means of the Main button (which is
 displayed when a file is highlighted).