- The `OPTION` command:
  - The `OPTION` command can be used to specify the location of an option tree or create an option tree (see the OPTION command explain file).
  - The `OPTION` command can be used to list the location of a defined option tree.

        nM> opt map
          MAP          = /home/student/projects/nxm/map/

  - The `OPTION` command can be used to list all available option trees.

        nM> opt
        Available Option Trees (<n> = index on path):
               AUDIO    = /home/student/nxm371/nxm/audio/
               DATABASE = /home/student/nxm371/nxm/database/
           <2> DSP      = /home/student/nxm371/nxm/dsp/
           <3> HWC      = /home/student/nxm371/nxm/hwc/
               ICE      = /home/student/nxm371/nxm/ice/ -> /xmopts/ice318/ <UnusedBackLink>
               MYOPT    = /home/student/nxm371/nxm/myopt/ -> /home/student/myopt123/
               SERVLET  = /home/student/nxm371/nxm/servlet/
           <4> SYS      = /home/student/nxm371/nxm/sys/
           <1> UCL      = /home/student/nxm371/nxm/ucl/
               XBC      = /home/student/nxm371/nxm/xbc/

    Any option trees located under `$NMROOT/nxm` (or linked to from there) are picked up automatically (in the above example these are highlighted in red). Any other option trees need to be specified using `OPTION`.
  - The `OPTION` command can be used define (declare) an option tree.

        nM> option train /home/student/nmopts/nxm/train/
          TRAIN          = /home/student/nmopts/nxm/train/