If you imagine DOM elements as each having a separate FSM and if you consider the possibility of entry/exit actions on each state, "idle, down" in the bottom le

If you imagine DOM elements as each having a separate FSM and if you consider the possibility of entry/exit actions on each state, "idle, down" in the bottom left could have an entry action that primes the system for drag & drop. Click down outside, release inside is exactly what D&D would have.