Players have no maximum hand size.
At the beginning of each player's draw step, that player draws an additional card, then discards a card.
10/4/2004 If the draw part of the effect is skipped due to a replacement effect, the discard part of the effect is not skipped.
10/1/2009 If multiple effects modify your hand size, apply them in timestamp order. For example, if you put Null Profusion (an enchantment that says your maximum hand size is two) onto the battlefield and then put Anvil of Bogardan onto the battlefield, you’ll have no maximum hand size. However, if those permanents entered the battlefield in the opposite order, your maximum hand size would be two.
4/15/2013 The triggered ability is put onto the stack after you have already drawn your card for the turn.
4/15/2013 If there are two Anvils on the battlefield, they trigger and resolve separately. This means that you first draw one card and discard one card, and then do it again. You do not draw two cards and then discard two cards.