<s>
In	O
the	O
X	B-Operating_System
Window	I-Operating_System
System	I-Operating_System
,	O
every	O
window	O
is	O
contained	O
within	O
another	O
window	O
,	O
called	O
its	O
parent	O
.	O
</s>
<s>
The	O
root	B-Device
window	I-Device
is	O
the	O
root	O
of	O
this	O
hierarchy	O
.	O
</s>
<s>
Since	O
every	O
window	O
covers	O
the	O
part	O
of	O
its	O
parent	O
it	O
is	O
staying	O
on	O
,	O
all	O
other	O
windows	O
appear	O
to	O
be	O
above	O
the	O
root	B-Device
window	I-Device
.	O
</s>
<s>
As	O
a	O
result	O
,	O
the	O
root	B-Device
window	I-Device
is	O
visible	O
as	O
the	O
part	O
of	O
the	O
screen	O
that	O
is	O
behind	O
all	O
other	O
windows	O
.	O
</s>
<s>
In	O
other	O
words	O
,	O
the	O
root	B-Device
window	I-Device
forms	O
the	O
background	O
of	O
the	O
screen	O
.	O
</s>
<s>
An	O
image	O
can	O
be	O
used	O
as	O
the	O
wallpaper	O
of	O
the	O
screen	O
by	O
setting	O
it	O
as	O
the	O
background	O
image	O
of	O
the	O
root	B-Device
window	I-Device
.	O
</s>
<s>
This	O
can	O
be	O
done	O
for	O
example	O
using	O
the	O
xsetroot	O
or	O
the	O
xv	B-Protocol
programs	O
.	O
</s>
<s>
The	O
direct	O
children	O
of	O
the	O
root	B-Device
window	I-Device
are	O
called	O
top-level	O
windows	O
.	O
</s>
<s>
These	O
windows	O
are	O
usually	O
drawn	O
with	O
a	O
decorative	O
frame	O
and	O
a	O
title	O
bar	O
(	O
which	O
are	O
actually	O
added	O
by	O
the	O
window	B-Application
manager	I-Application
)	O
.	O
</s>
<s>
The	O
top-level	O
windows	O
are	O
,	O
informally	O
,	O
the	O
regular	O
windows	O
in	O
the	O
terminology	O
of	O
most	O
GUIs	B-Application
.	O
</s>
<s>
The	O
properties	O
of	O
the	O
root	B-Device
window	I-Device
are	O
sometimes	O
used	O
as	O
a	O
rudimentary	O
form	O
of	O
inter-client	O
communication	O
means	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
cut	B-Device
buffers	I-Device
are	O
properties	O
of	O
the	O
root	B-Device
window	I-Device
that	O
are	O
used	O
for	O
copying	O
selected	O
text	O
from	O
a	O
window	O
to	O
another	O
,	O
and	O
the	O
dwm	B-Language
window	B-Application
manager	I-Application
displays	O
the	O
root	B-Device
window	I-Device
's	O
name	O
in	O
a	O
status	O
area	O
.	O
</s>
<s>
The	O
X	B-Device
resources	I-Device
are	O
also	O
stored	O
,	O
during	O
execution	O
,	O
in	O
a	O
property	O
of	O
the	O
root	B-Device
window	I-Device
.	O
</s>
<s>
The	O
swm	B-Device
window	B-Application
manager	I-Application
introduced	O
the	O
virtual	O
root	B-Device
window	I-Device
.	O
</s>
<s>
From	O
the	O
point	O
of	O
view	O
of	O
the	B-Protocol
X	I-Protocol
protocol	I-Protocol
,	O
this	O
is	O
a	O
regular	O
window	O
.	O
</s>
<s>
However	O
,	O
X	B-Application
window	I-Application
managers	I-Application
using	O
the	O
virtual	O
root	B-Device
window	I-Device
reparent	O
all	O
windows	O
to	O
it	O
instead	O
of	O
to	O
the	O
real	O
root	B-Device
window	I-Device
.	O
</s>
<s>
Virtual	O
root	B-Device
windows	I-Device
are	O
mainly	O
used	O
by	O
re-parenting	B-Device
window	I-Device
managers	I-Device
,	O
for	O
example	O
,	O
for	O
realizing	O
a	O
number	O
of	O
virtual	B-Application
desktops	I-Application
the	O
user	O
can	O
switch	O
between	O
.	O
</s>
<s>
Other	O
clients	O
(	O
beside	O
the	O
window	B-Application
manager	I-Application
)	O
may	O
need	O
to	O
use	O
the	O
virtual	O
root	B-Device
window	I-Device
.	O
</s>
<s>
The	O
identifier	O
of	O
this	O
window	O
can	O
be	O
found	O
in	O
a	O
window	O
property	O
named	O
__SWM_VROOT	O
in	O
a	O
direct	O
child	O
of	O
the	O
real	O
root	B-Device
window	I-Device
.	O
</s>
<s>
Technically	O
,	O
many	O
programs	O
use	O
the	O
macros	O
for	O
finding	O
the	O
root	B-Device
windows	I-Device
as	O
redefined	O
by	O
an	O
include	O
file	O
named	O
vroot.h.	O
</s>
<s>
The	O
freedesktop	B-Application
window	B-Application
manager	I-Application
specification	O
requires	O
a	O
property	O
named	O
_NET_VIRTUAL_ROOTS	O
of	O
the	O
real	O
root	B-Device
window	I-Device
to	O
contain	O
a	O
list	O
of	O
the	O
windows	O
that	O
are	O
acting	O
as	O
virtual	O
root	B-Device
windows	I-Device
;	O
the	O
virtual	O
root	B-Device
window	I-Device
that	O
is	O
currently	O
active	O
can	O
be	O
found	O
in	O
the	O
property	O
_NET_CURRENT_DESKTOP	O
of	O
the	O
real	O
root	B-Device
window	I-Device
.	O
</s>
<s>
The	O
virtual	O
root	B-Device
window	I-Device
is	O
used	O
by	O
the	O
window	B-Application
managers	I-Application
swm	B-Device
,	O
tvtwm	B-Device
,	O
amiwm	B-Device
,	O
and	O
enlightenment	B-Application
.	O
</s>
<s>
Other	O
systems	O
such	O
as	O
KDE	B-Application
use	O
a	O
virtual	O
background	O
window	O
(	O
which	O
contains	O
the	O
icons	O
,	O
for	O
example	O
)	O
but	O
do	O
not	O
reparent	O
the	O
other	O
windows	O
to	O
this	O
one	O
.	O
</s>
<s>
The	O
virtual	O
root	B-Device
window	I-Device
is	O
also	O
used	O
by	O
XScreenSaver	B-General_Concept
:	O
when	O
the	O
screensaver	O
is	O
activated	O
,	O
this	O
program	O
creates	O
a	O
virtual	O
root	B-Device
window	I-Device
,	O
places	O
it	O
at	O
the	O
top	O
of	O
all	O
other	O
windows	O
,	O
and	O
calls	O
one	O
of	O
its	O
hacks	O
(	O
modules	O
)	O
,	O
which	O
finds	O
the	O
virtual	O
root	B-Device
window	I-Device
and	O
draws	O
in	O
it	O
.	O
</s>
