2D: 20-21 balanced or semi-balanced

• 2H/S: relay with better spades/hearts
  
• 2NT: relay after after which the developments continue as after 2NT opening
  
• 2NT/3C: transfer to clubs/diamonds (usually for a sign-off)
• 4K: 5+5+ in the majors
  

Responses after opponent's DBL

• Pass: The usual bid
• RDBL/2H/2S/3C: transfer (usually for sign-off)
  

Responses after opponent's over-call

• Pass: Weak
• DBL: Some strength
• Other: Natural