Does the mouse cursor have inventory?

Hello good, I have a question, it happens that when we drag an item from an inventory it follows the mouse cursor and I would like to see if there is a way to obtain the items in the cursor is to select the items that we drag, I suppose that like the inventory of the player and the armor inventory the items that we drag must be stored in a slot and that is what I want to know if so what is the ID of the slot in question if someone can help me or knows a way thanks.