How is the plotly 3D volume plot generated?

Question

I've come across the following code in an example of the plotly 3D volume plots:

import plotly.graph_objects as go
import numpy as np


x1 = np.linspace(-4, 4, 9) 
y1 = np.linspace(-5, 5, 11) 
z1 = np.linspace(-5, 5, 11) 

X, Y, Z = np.meshgrid(x1, y1, z1)

values = (np.sin(X**2 + Y**2))/(X**2 + Y**2)

fig = go.Figure(data=go.Volume(
    x=X.flatten(),
    y=Y.flatten(),
    z=Z.flatten(),
    value=values.flatten(),
    opacity=0.1,
))

fig.show()

As I understand it, the 'x', 'y' and 'z' are what form the base 3D mesh cube grid and I presume that the 'value' forms the actual shape within the 3D mesh. The issue is I don't understand exactly how the 'value' field is being used to form the inner volume and the documentation doesn't seem to be at all helpful.

I initially believed that each row (or column) in the 3D values array represented a point within the mesh, but from experimentation that doesn't seem to be what's happening. Can someone please explain how this works?