Penalty (re)double

Generally, a double of opponent's bid at or above (3H) is for penalty, except the following:

• An invitational double of (3H)
• A double of opponent's (4m) opening is for takeout
• A lead-directing double of opponent's unnatural bid
• Using the PDF rule against opponent's interference

In addition, the following doubles, although below (3H), are also for penalty.

• Some doubles of (1NT) -- see here for details
• A double of (2NT), except when it is an invitational double
• A fit has been established and the double is not invitational