Click on the button to direct MMS to look for source files, description
 files and included files in the current default CMS library as well as the
 specified directories.

 When you specify Use CMS, and the source in the CMS library is newer, MMS
 fetches it from the CMS library.  If the source in the CMS library is older,
 MMS instead used the source in the specified directory.

 CMS must be installed on your system.