def expand_pathseg(handle)
      return handle unless handle.is_a?(Symbol)
      pathsegs = ROOT_PATHS[handle] or raise ArgumentError,
        "Don't know how to expand path reference '#{handle.inspect}'."
      pathsegs.map { |ps| expand_pathseg(ps) }.flatten
    end
def expand_pathseg(handle)
      return handle unless handle.is_a?(Symbol)
      pathsegs = ROOT_PATHS[handle] or raise ArgumentError,
        "Don't know how to expand path reference '#{handle.inspect}'."
      pathsegs.map { |ps| expand_pathseg(ps) }.flatten
    end
A T T E N Z I O N E   A R E A   P R O T E T T A
 Recursively expand a path handle.

 @return [Array<String>]
   An array of path segments, suitable for .join

 @api public