#### Explain Files

Every command has an explain file. Below is an annotated explain file template that shows common conventions. First, it shows the command name, then parameters and switches, and finally a brief explanation of how to use the command:

    nM> expl option
    OPTION  displays or defines an option tree path
    [NAME]      - Name of the option tree
    [PATH]      - Path to the named option tree (or physical path
                 when /CREATE is used and OPT.name is a link)

    This command is used to define a NeXtMidas option tree path.
    Option trees in NeXtMidas are implemented using Java packages.
    The root package name is "nxm", followed by the "option name",
    and then functional subdirectories. Use the /CREATE switch
    after OPT.name has been defined to create an option tree.
    .
    .
    At run-time, the Midas class loader will follow the option
    tree paths set up using the OPTION and the PATH commands
    within the NeXtMidas shell. These are typically set up in the
    nmstartup.mm macro.

    startmacro
      option ice "/user/xmopts/ice279/"
      option geo "/user/geo100/"
      path set ice geo
    endmacro

You can read the explain file of any NeXtMidas command by typing `explain,` or`expl,` and the command name after the NeXtMidas prompt`(nM>):`

    nM> expl <command name>