code: func RegisterCommand(mode string, makeCmd func(Flags *flag.FlagSet) CommandRunner) {
  	RegisterMode(mode, makeCmd)
  	asNewCommand[mode] = true
  }
docs: // RegisterCommand adds a mode to the list of modes for the main command, and
  // also specifies that this mode is just another executable that runs as a new
  // cmdmain command. The executable to run is determined by the LookPath implementation
  // for this mode.