<s>
Z-order	O
is	O
an	O
ordering	O
of	O
overlapping	O
two-dimensional	O
objects	O
,	O
such	O
as	O
windows	O
in	O
a	O
stacking	B-Device
window	I-Device
manager	I-Device
,	O
shapes	O
in	O
a	O
vector	B-Application
graphics	I-Application
editor	I-Application
,	O
or	O
objects	O
in	O
a	O
3D	O
application	O
.	O
</s>
<s>
Some	O
window	B-Application
managers	I-Application
allow	O
interaction	O
with	O
windows	O
while	O
they	O
are	O
not	O
in	O
the	O
foreground	O
,	O
while	O
others	O
will	O
bring	O
a	O
window	O
to	O
the	O
front	O
whenever	O
it	O
receives	O
input	O
from	O
the	O
user	O
.	O
</s>
<s>
An	O
HTML	O
page	O
can	O
use	O
CSS	B-Language
to	O
specify	O
the	O
Z-order	O
so	O
that	O
some	O
objects	O
can	O
be	O
layered	O
over	O
others	O
.	O
</s>
<s>
The	O
actual	O
number	O
assigned	O
to	O
a	O
particular	O
place	O
in	O
the	O
Z-order	O
is	O
sometimes	O
known	O
as	O
the	O
z-index	B-General_Concept
.	O
</s>
<s>
In	O
particular	O
the	O
CSS	B-Language
property	O
that	O
sets	O
the	O
stack	O
order	O
of	O
specific	O
elements	O
is	O
known	O
as	O
the	O
z-index	B-General_Concept
.	O
</s>
<s>
z-index	B-General_Concept
only	O
works	O
on	O
elements	O
that	O
have	O
a	O
position	O
value	O
(	O
e.g.	O
</s>
<s>
position	O
:	O
relative	O
;	O
)	O
and	O
for	O
many	O
coders	O
,	O
this	O
one	O
of	O
the	O
first	O
things	O
to	O
investigate	O
when	O
debugging	O
why	O
the	O
z-index	B-General_Concept
is	O
n't	O
working	O
.	O
</s>
<s>
Like	O
all	O
other	O
CSS	B-Language
properties	O
,	O
it	O
can	O
be	O
set	O
with	O
JavaScript	B-Language
as	O
well	O
with	O
the	O
following	O
syntax	O
:	O
</s>
