<s>
XBL	B-Application
(	O
XML	B-Application
Binding	I-Application
Language	I-Application
)	O
is	O
an	O
XML-based	O
markup	O
language	O
for	O
altering	O
the	O
behavior	O
of	O
XUL	B-Application
widgets	O
.	O
</s>
<s>
It	O
was	O
devised	O
at	O
Netscape	B-Protocol
in	O
the	O
late	O
1990s	O
as	O
an	O
extension	O
of	O
XUL	B-Application
.	O
</s>
<s>
The	O
primary	O
use	O
of	O
XBL	B-Application
was	O
in	O
the	O
Firefox	B-Application
web	I-Application
browser	I-Application
,	O
but	O
Mozilla	B-Operating_System
deprecated	O
it	O
in	O
2017	O
and	O
completely	O
removed	O
it	O
from	O
Firefox	B-Application
in	O
2019	O
.	O
</s>
<s>
However	O
,	O
the	O
UXP	O
fork	B-Application
of	O
Firefox	B-Application
intends	O
to	O
continue	O
supporting	O
XBL	B-Application
indefinitely	O
.	O
</s>
<s>
Mozilla	B-Operating_System
attempted	O
to	O
standardize	O
XBL	B-Application
2.0	I-Application
via	O
W3C	O
in	O
2007	O
,	O
but	O
due	O
to	O
lack	O
of	O
interest	O
from	O
other	O
web	B-Application
browser	I-Application
vendors	O
,	O
abandoned	O
it	O
in	O
2012	O
.	O
</s>
<s>
The	O
Shadow	O
DOM	O
specification	O
acknowledges	O
XBL	B-Application
as	O
a	O
strong	O
influence	O
.	O
</s>
<s>
XUL	B-Application
defines	O
the	O
user	B-Application
interface	I-Application
layout	O
of	O
an	O
application	B-Application
.	O
</s>
<s>
CSS	B-Language
rules	O
can	O
be	O
used	O
to	O
change	O
the	O
appearance	O
of	O
various	O
XUL	B-Application
elements	O
.	O
</s>
<s>
But	O
XBL	B-Application
is	O
needed	O
to	O
alter	O
the	O
behavior	O
of	O
a	O
XUL	B-Application
widget	O
,	O
such	O
as	O
a	O
scroll	O
bar	O
.	O
</s>
<s>
An	O
XBL	B-Application
file	O
contains	O
bindings	B-General_Concept
,	O
each	O
of	O
which	O
describes	O
the	O
behavior	O
of	O
a	O
XUL	B-Application
widget	O
.	O
</s>
<s>
The	O
root	O
element	O
of	O
an	O
XBL	B-Application
file	O
is	O
the	O
<bindings> element, which contains one or more <binding>	O
elements	O
.	O
</s>
<s>
Each	O
<binding>	O
element	O
declares	O
one	O
binding	O
,	O
which	O
can	O
be	O
attached	O
to	O
any	O
XUL	B-Application
element	O
.	O
</s>
<s>
A	O
binding	O
is	O
assigned	O
to	O
an	O
element	O
by	O
setting	O
the	O
CSS	B-Language
property	O
-moz-binding	O
to	O
the	O
URL	O
of	O
the	O
binding	O
's	O
file	O
.	O
</s>
