================================================================================
Background - simple
================================================================================

printf "one" &

--------------------------------------------------------------------------------

(program
  (command
    name: (word)
    argument: (double_quote_string)))

================================================================================
Background - multiple
================================================================================

printf "one" & echo &

--------------------------------------------------------------------------------

(program
  (command
    name: (word)
    argument: (double_quote_string))
  (command
    name: (word)))

================================================================================
Background - with redirect
================================================================================

printf > file &

--------------------------------------------------------------------------------

(program
  (redirected_statement
    (command
      name: (word))
    (file_redirect
      operator: (direction)
      destination: (word))))
