If I remember well on a real upright there is a mechanism to block the celeste pedal down.
Is it indeed possible for a player with a real piano to use the celeste pedal smoothly between up and down?

Of course I hear the timbre difference but I would like to know which physical action this parameter is supposed to emulate.
The pressure of the felt on the strings as if the player would continuously press the pedal from up to down?
The thickness of the felt (someone mentions this on this forum)?
Something else?