POKEDECHASH axmud-object-property, expression

   Synopsis:
      Decrements a key-value pair in an Axmud internal hash property

   Notes:
      POKE gives Axbasic scripts access to some of Axmud's internal data (see
         the help for the POKE statement for a full explanation).
      POKEDECHASH is similar to POKE, but it only modifies hash properties such
         as "world.current.currencyHash". It cannot be used to modify a scalar
         property such as "world.current.longName", a list property such as
         "world.current.doorPatternList" or a Perl object such as
         "world.current".
      POKEDECHASH modifies a key-value pair in the hash property. 'expression'
         is a key which must exist in the hash. POKEINCHASH decreases the key's
         corresponding value - which must be an integer - by 1.
      Much of Axmud's internal data is read-only, and cannot be modified with
         POKE or with this statement. If you try to modify a read-only property
         you will get an 'operation failure' error.

   Warning:
      Do not try to modify Axmud's internal data unless you know what you are
         doing. Read the Axmud manual before you try to POKE anything. (The
         examples below are safe, but backup your data first.)

   Examples:
      ! On DeadSouls, decrease the relative value of a platinum coin (stored as
      ! a key-value pair, where the key is "platinum" and the value is 1)
      POKEINCHASH "world.current.currencyHash", "platinum"
      ! The value must not fall below 1!
      PEEKSHOW value = "world.current.currencyHash", "platinum"
      IF value < 1 THEN
         POKEADD "world.current.currencyHash", "platinum", 1
      END IF
