A PannerNode always has exactly one input and one output: the input can be mono or stereo but the output is always stereo (2 channels); you can't have panning effects without at least two audio channels!
An AudioParam whose value is the X component of the direction in which the audio source is facing, in 3D Cartesian coordinate space.
The easiest use case to imagine for this capability is realistic alterations in how an audio source will sound as you move around it in a 3D environment like a first-person game.
An AudioParam whose value is the Y component of the direction the audio source is facing, in 3D Cartesian coordinate space.
An AudioParam whose value is the X coordinate of the audio source's position, in 3D Cartesian coordinates.
An AudioParam whose value is the Y coordinate of the audio source's position, in 3D Cartesian coordinates.
An AudioParam whose value is the Z coordinate of the audio source's position, in 3D Cartesian coordinates.