All of the bridge book about competitive bidding I have define 3♦ as single suit invitation but it seems like a mordern approach is treat this 3♦ as fit showing jump.
Could anyone tell me(or tell me where can I find) the detail of this convention? My question include
1. What's the main purpose/advantage of this bid?
2. What's the rough strength/suit quality/trump qaulity of this bid?
3. Is this on if I jump to 4 level(partner simple overcall 2 level)? Is anything changes if responder enters the auction?

Help
