Proper signing. As much for what it implies as for the player himself - and Tonali himself is no slouch. Fast, strong, relentless. A Premier League-proven box to box midfielder in the Daniele De Rossi mould, and we're getting him in his absolute prime at 26.
But it's more what it means that impresses me. For once, the club have decided to equip the manager with exactly who he wants, when he wants them - well before pre-season starts.
A full pre-season with most of his first-choice signings in place, followed by a season with one game a week to embed his ideas and tactics.
De Zerbi has no excuses not to deliver. This is the best chance he's ever had at building a squad that is tailor-made to his football, and Tonali sounds like the centrepiece of his project here. The club have put their money where their mouth is, and have put total faith in him - up to him now to prove that faith is justified.
I can't wait to see this play out.