what is Logical Display Surface in Screen Capture API of browser?

Question

I'm wondering that what is Logical Display Surface actually ?

In MDN docs:
A logical display surface is one which is in part or completely obscured, either by being overlapped by another object to some extent, or by being entirely hidden or offscreen. How these are handled by the Screen Capture API varies. Generally, the browser will provide an image which obscures the hidden portion of the logical display surface in some way, such as by blurring or replacing with a color or pattern. This is done for security reasons, as the content that cannot be seen by the user may contain data which they do not want to share.

But when I add logicalSurface: true into video constrant, there is nothing changed. When I set it to logicalSurface: false, there is also nothing changed. Can everyone give me a real example for this ?

const constraints = {
    video: {
                logicalSurface: true // True and False are same :'(
    },
    audio: true
}
const stream = await navigator.mediaDevices.getDisplayMedia(constraints);
localVideo.srcObject = stream;

Thank you.