When a Format 6 DISPLAY statement is specified, environment-value
  receives the value stored in envlog-value. The environment variable
  or logical is the one named by a Format 5 DISPLAY statement. See
  ENVIRONMENT-VALUE in the SPECIAL-NAMES paragraph.

  Format 6 -

   DISPLAY envlog-value UPON environment-value

      [ ON EXCEPTION stment ]
      [ NOT ON EXCEPTION stment2 ]

      [ END-DISPLAY ]