### When a command is launched

                                                | 0' set to contain the
|-----------------------------------| line exactly as typed
. <command> <thing1> <thing2> ... <thingk>
|         |        |           |      |
|         |        |           |      +--> <k+1>' set to contain ""
|         |        |           |                   (nothing)
|         |        |           |
|         |        |           +--> <k>' set to contain "<thingk>"
|         |        |
|         |        |
|         |        +--> 2' set to contain "<thing2>"
|         |
|         +--> 1' set to contain "<thing1>"
|        |----------------------------------------------------|
|                                |
|                                |
|          *' set to contain "<thing> <thing2> ... <thingk>"
|