PCAC> SPAWN MAIL
  You have 1 new message.
  MAIL> READ\NEW
   . . .
  MAIL> EXIT
  %PCA-I-RETURNED, control returned to process CARRELL
  PCAC>

      This command spawns a subprocess that runs the MAIL program.
      When you exit from MAIL, you return to the original PCA
      session.

  PCAC> SPAWN
  $ TYPE MUMBLE.DAT
   . . .
  $ LOGOUT
         Process CARRELL_1 logged out at 29-FEB-1985 14:10:43.55
  %PCA-I-RETURNED, control returned to process CARRELL
  PCAC>

      This command spawns a subprocess. Since you did not specify a
      DCL command on the SPAWN command, the subprocess prompts for
      DCL commands. When you log out of the subprocess, you return to
      the PCA session.