draw step and priority

[TheWhiteDragon]

In the draw step, my opponent draws a card.  When he moves into main phase, do I get a chance to play effects at the end of his draw step, or does he go from end of upkeep straight through main phase without ever passing priority?  For instance, can I wait until after he draws to cast extirpate and hopefully snag the extra card he drew....or does he get to cast spells before I can extirpate?

[BC]

You get priority in the draw step.  People do that with Vendillion Clique all the time.

[Clariax]

Both players can cast spells during the draw step.  The active player has a chance first, then after he passes priority, the nonactive player has a chance.  So he can, if he wishes cast an instant during his draw step before you have an opportunity to cast Extirpate, but you will get a chance ot cast Extirpate before he moves to his draw step.

[Samoht]

Both players can cast spells during the draw step.  The active player has a chance first, then after he passes priority, the nonactive player has a chance.  So he can, if he wishes cast an instant during his draw step before you have an opportunity to cast Extirpate, but you will get a chance ot cast Extirpate before he moves to his draw step.

Moves out of his draw step*