- The Option Tree Path:
  - The path is the list of option trees that are in use.
    - The SYS option tree must always be included.
  - The path is ordered such that option trees with higher standing appear first.
    - If a command typed in matches commands in multiple option trees the one in the option tree listed first will be used.
      - This feature can be overridden by explicitly indicating the option tree to be used. This is done by appending "`;<opt>`" at the end of the command name (e.g. `FFT;SYS`).
    - The SYS option tree is always last.
  - The `OPT` table maps the name of each option tree to its location on disk (or on the web).
    - Option trees that come bundled with NeXtMidas and those linked to under `$NMROOT/nxm/` do not need to be included in the `OPT` table. (More on this later.)

Don't Make This Mistake:
Note: Option trees can not be named PATH, CLASSPATH, orNXM since these are special reserved entries in the `OPT` table. Option tree names must be unique. Additionally the use of the names OPT (the generic name used in many examples) and XM (used when linking to X-Midas) should be avoided.