Key/mouse combination to interact with clickable things in 3D world. More precisely, this input will activate pointing device sensors in VRML/X3D, which are used to touch (click) or drag 3D things. By default this is left mouse button click.
Key/mouse combination to operate on Player and it's inventory. They are used only when Player is assigned, and only when it's not Dead and not Blocked (see T3DAlive.Dead, TPlayer.Blocked). Also other TCastleAbstractViewport rules for processing inputs must be satisfied, of course (TCastleAbstractViewport must exist, according to TCastleAbstractViewport.GetExists, and not be paused, see TCastleAbstractViewport.Paused). The event must also not be handled first by something else, like camera.