marker command
    (A) Function
        Outputting/changing a marker position. 
    (B) Format
         marker  [ <position> ]
    (C) Parameter
        <position>
           Designate a destination of a marker position. 
           A destination is an arbitrary facility. 
           If <position> is not specified, this command 
           returns the current marker position. 
    (D) Notes
        The first install command sets a current position 
        to the root ('/') of a simulation image.
    (E) Related items
        move command