This is an invisible window on the top layer. Here is the result of xwininfo
xwininfo: Window id: 0x3c00003 (has no name)
Absolute upper-left X: 100 Absolute upper-left Y: 100 Relative upper-left X: 0 Relative upper-left Y: 0 Width: 320 Height: 200 Depth: 24 Visual: 0x21 Visual Class: TrueColor Border width: 0 Class: InputOutput Colormap: 0x20 (installed) Bit Gravity State: ForgetGravity Window Gravity State: NorthWestGravity Backing Store State: NotUseful Save Under State: no Map State: IsViewable Override Redirect State: no Corners: +100+100 -604+100 -604-300 +100-300 -geometry 320x200+100+100
This is an invisible window on the top layer. Here is the result of xwininfo
xwininfo: Window id: 0x3c00003 (has no name)
Absolute upper-left X: 100
Absolute upper-left Y: 100
Relative upper-left X: 0
Relative upper-left Y: 0
Width: 320
Height: 200
Depth: 24
Visual: 0x21
Visual Class: TrueColor
Border width: 0
Class: InputOutput
Colormap: 0x20 (installed)
Bit Gravity State: ForgetGravity
Window Gravity State: NorthWestGravity
Backing Store State: NotUseful
Save Under State: no
Map State: IsViewable
Override Redirect State: no
Corners: +100+100 -604+100 -604-300 +100-300
-geometry 320x200+100+100