How to enter multiple include files with the Options > Includes tab in Calibre Interactive?

Version 1

    In Calibre Interactive  the Setup > Options > Includes tab says to "specify one per line".
    When entering the include file names by hand, hitting <return> does not put the cursor on a new line.

    Use <control> <enter> at the end of each name.
    That will get a new line on which to start the next include file name.