Madness was originally a fairly complex series of triggers so that
  the spell could be played using the system of priority.  Since then,
  other cards have been created that allow a spell to be played when
  no player has priority.  This created the opportunity to "clean up"
  the madness rules.  So, whereas before it was possible under some
  circumstances to play a land inbetween the discard of the card and
  playing the card for its madness cost, these days it's much simpler:

  - playing or resolving a spell or ability, or dealing with the discard
  to maximum hand size at cleanup, causes you to discard a card.

  - the madness ability on the card allows you to replace the card going
  to the graveyard with removing it from the game.  Doing so triggers
  an ability: "you may play this card for its mana cost. If you don't,
  put it into your graveyard."  Since the madness ability retains the
  term 'discard' for this new event, it also triggers anything that
  triggers on a discard.

  - when a player would next get priority, the triggered ability goes on
  the stack.  When it resolves, you choose whether to play the removed
  card or not.  If so, its cost will be the madness cost instead of the
  mana cost.  If not, it's put into your graveyard.

Some parts © 2009 Advameg, Inc.