Disturb Opponent's Forcing No-Trump
We discussed the weakness in 2/1 bidding is the forcing NT. We abandoned the Forcing NT in favor of retaining the natural 6-9, no support meaning. However, a large percentage of your opponents will still be playing forcing NT (or semi-forcing).
Disturb Opponent's Forcing NT (DONT) is a convention to exploit the opponent's uncertainity of the value of the Forcing NT bid. It is important to compete with a wide variety of hands, especially hands that you would like to tip your partner into what lead to make. The nature of the 1NT bid, means that the opponents are not likely to be in a position to punish your interference at the 2-level with a penalty double.
After the opponent's forcingNT an overcall is one under the suit overcaller wants to show - a transfer request.
The transfer request here, allows the overcaller a rebid. This means that they can be weak or strong when making an overcall. The one under make disrupt the opponent (because that was the bid they wanted to make, and perhaps a 'double' doesn't convey the shape/strength of the opening hand).
The Advancer should complete the transfer at the 2-level. If the opener does bid (forcing the advancer to the 3-level), then the Advancer bids with a near opening strength hand (10+ HCP). Remember in a forcing NT auction, they have passed after the opening bid and before the 1NT bid. It is possible that they have a good hand, but were unable to make a call over the opening bid. That case might be holding strength/length in the opening suit. Such hands (with poor support for the overcaller) may choose to bid 2NT instead of the transfer suit.