<s>
XSL-FO	B-Language
(	O
XSL	B-Language
Formatting	I-Language
Objects	I-Language
)	O
is	O
a	O
markup	O
language	O
for	O
XML	B-Protocol
document	I-Protocol
formatting	O
that	O
is	O
most	O
often	O
used	O
to	O
generate	O
PDF	B-Application
files	I-Application
.	O
</s>
<s>
XSL-FO	B-Language
is	O
part	O
of	O
XSL	B-Language
(	O
Extensible	B-Language
Stylesheet	I-Language
Language	I-Language
)	O
,	O
a	O
set	O
of	O
W3C	O
technologies	O
designed	O
for	O
the	O
transformation	O
and	O
formatting	O
of	O
XML	B-Protocol
data	O
.	O
</s>
<s>
The	O
other	O
parts	O
of	O
XSL	B-Language
are	O
XSLT	B-Application
and	O
XPath	B-Language
.	O
</s>
<s>
Version	O
1.1	O
of	O
XSL-FO	B-Language
was	O
published	O
in	O
2006	O
.	O
</s>
<s>
XSL-FO	B-Language
is	O
considered	O
feature	O
complete	O
by	O
W3C	O
:	O
the	O
last	O
update	O
for	O
the	O
Working	O
Draft	O
was	O
in	O
January	O
2012	O
,	O
and	O
its	O
Working	O
Group	O
closed	O
in	O
November	O
2013	O
.	O
</s>
<s>
Unlike	O
the	O
combination	O
of	O
HTML	B-Language
and	O
CSS	B-Language
,	O
XSL-FO	B-Language
is	O
a	O
unified	O
presentational	O
language	O
.	O
</s>
<s>
It	O
has	O
no	O
semantic	O
markup	O
as	O
this	O
term	O
is	O
used	O
in	O
HTML	B-Language
.	O
</s>
<s>
And	O
,	O
unlike	O
CSS	B-Language
which	O
modifies	O
the	O
default	O
presentation	O
of	O
an	O
external	O
XML	B-Protocol
or	O
HTML	B-Language
document	O
,	O
it	O
stores	O
all	O
of	O
the	O
document	O
's	O
data	O
within	O
itself	O
.	O
</s>
<s>
The	O
general	O
idea	O
behind	O
XSL-FO	B-Language
'	O
s	O
use	O
is	O
that	O
the	O
user	O
writes	O
a	O
document	O
,	O
not	O
in	O
FO	O
,	O
but	O
in	O
an	O
XML	B-Protocol
language	O
.	O
</s>
<s>
XHTML	B-Language
,	O
DocBook	B-Protocol
,	O
and	O
TEI	B-Language
are	O
all	O
possible	O
examples	O
.	O
</s>
<s>
Then	O
,	O
the	O
user	O
obtains	O
an	O
XSLT	B-Application
transform	O
,	O
either	O
by	O
writing	O
one	O
themselves	O
or	O
by	O
finding	O
one	O
for	O
the	O
document	O
type	O
in	O
question	O
.	O
</s>
<s>
This	O
XSLT	B-Application
transform	O
converts	O
the	O
XML	B-Protocol
into	O
XSL-FO	B-Language
.	O
</s>
<s>
Once	O
the	O
XSL-FO	B-Language
document	O
is	O
generated	O
,	O
it	O
is	O
then	O
passed	O
to	O
an	O
application	O
called	O
an	O
FO	O
processor	O
.	O
</s>
<s>
FO	O
processors	O
convert	O
the	O
XSL-FO	B-Language
document	O
into	O
something	O
that	O
is	O
readable	O
,	O
printable	O
or	O
both	O
.	O
</s>
<s>
The	O
most	O
common	O
output	O
of	O
XSL-FO	B-Language
is	O
a	O
PDF	B-Application
file	I-Application
or	O
as	O
PostScript	B-Language
,	O
but	O
some	O
FO	O
processors	O
can	O
output	O
to	O
other	O
formats	O
like	O
RTF	O
files	O
or	O
even	O
just	O
a	O
window	O
in	O
the	O
user	O
's	O
GUI	O
displaying	O
the	O
sequence	O
of	O
pages	O
and	O
their	O
contents	O
.	O
</s>
<s>
The	O
XSLT	B-Application
language	O
itself	O
was	O
originally	O
conceived	O
only	O
for	O
this	O
purpose	O
;	O
it	O
is	O
now	O
in	O
widespread	O
use	O
for	O
more	O
general	O
XML	B-Protocol
transformations	O
.	O
</s>
<s>
This	O
transformation	O
step	O
is	O
taken	O
so	O
much	O
for	O
granted	O
in	O
XSL-FO	B-Language
that	O
it	O
is	O
not	O
uncommon	O
for	O
people	O
to	O
call	O
the	O
XSLT	B-Application
that	O
turns	O
XML	B-Protocol
into	O
XSL-FO	B-Language
the	O
actual	O
XSL-FO	B-Language
document	O
itself	O
.	O
</s>
<s>
Even	O
tutorials	O
on	O
XSL-FO	B-Language
tend	O
to	O
be	O
written	O
with	O
XSLT	B-Application
commands	O
around	O
the	O
FO	O
processing	O
instructions	O
.	O
</s>
<s>
The	O
XSLT	B-Application
transformation	O
step	O
is	O
exceptionally	O
powerful	O
.	O
</s>
<s>
An	O
XSL-FO	B-Language
document	O
is	O
not	O
like	O
a	O
PDF	B-Application
or	O
a	O
PostScript	B-Language
document	O
.	O
</s>
<s>
The	O
XSL-FO	B-Language
specification	O
even	O
allows	O
different	O
FO	O
processors	O
to	O
have	O
varying	O
responses	O
with	O
regard	O
to	O
the	O
resultant	O
generated	O
pages	O
.	O
</s>
<s>
There	O
are	O
other	O
cases	O
where	O
the	O
XSL-FO	B-Language
specification	O
explicitly	O
allows	O
FO	O
processors	O
some	O
degree	O
of	O
choice	O
with	O
regard	O
to	O
layout	O
.	O
</s>
<s>
This	O
is	O
because	O
the	O
general	O
purpose	O
behind	O
XSL-FO	B-Language
is	O
to	O
generate	O
paged	O
,	O
printed	O
media	O
.	O
</s>
<s>
XSL-FO	B-Language
documents	O
themselves	O
are	O
usually	O
used	O
as	O
intermediaries	O
,	O
mostly	O
to	O
generate	O
either	O
PDF	B-Application
files	I-Application
or	O
a	O
printed	O
document	O
as	O
the	O
final	O
form	O
to	O
be	O
distributed	O
.	O
</s>
<s>
This	O
is	O
as	O
opposed	O
to	O
how	O
HTML	B-Language
is	O
generated	O
and	O
distributed	O
as	O
a	O
final	O
form	O
directly	O
to	O
the	O
user	O
.	O
</s>
<s>
Distributing	O
the	O
final	O
PDF	B-Application
rather	O
than	O
the	O
formatting	O
language	O
input	O
(	O
whether	O
HTML/CSS	O
or	O
XSL-FO	B-Language
)	O
means	O
on	O
the	O
one	O
hand	O
that	O
recipients	O
are	O
n't	O
affected	O
by	O
the	O
unpredictability	O
resulting	O
from	O
differences	O
among	O
formatting	O
language	O
interpreters	O
,	O
while	O
on	O
the	O
other	O
hand	O
means	O
that	O
the	O
document	O
cannot	O
easily	O
adapt	O
to	O
different	O
recipient	O
needs	O
,	O
such	O
as	O
different	O
page	O
size	O
or	O
preferred	O
font	O
size	O
,	O
or	O
tailoring	O
for	O
on-screen	O
versus	O
on-paper	O
versus	O
audio	O
presentation	O
.	O
</s>
<s>
The	O
XSL-FO	B-Language
language	O
was	O
designed	O
for	O
paged	O
media	O
;	O
as	O
such	O
,	O
the	O
concept	O
of	O
pages	O
is	O
an	O
integral	O
part	O
of	O
XSL-FO	B-Language
'	O
s	O
structure	O
.	O
</s>
<s>
XSL-FO	B-Language
does	O
not	O
easily	O
handle	O
the	O
tight	O
restrictions	O
of	O
magazine	O
layout	O
;	O
indeed	O
,	O
in	O
many	O
cases	O
,	O
it	O
lacks	O
the	O
ability	O
to	O
express	O
some	O
forms	O
of	O
said	O
layout	O
.	O
</s>
<s>
These	O
features	O
are	O
comparable	O
to	O
CSS	B-Language
's	O
layout	O
features	O
,	O
though	O
some	O
of	O
those	O
features	O
are	O
expected	O
to	O
be	O
built	O
by	O
the	O
XSLT	B-Application
.	O
</s>
<s>
XSL-FO	B-Language
documents	O
are	O
XML	B-Protocol
documents	I-Protocol
,	O
but	O
they	O
do	O
not	O
have	O
to	O
conform	O
to	O
any	O
DTD	B-Language
or	O
schema	O
.	O
</s>
<s>
XSL-FO	B-Language
documents	O
contain	O
two	O
required	O
sections	O
.	O
</s>
<s>
Blocks	O
and	O
inline	O
elements	O
function	O
in	O
much	O
the	O
same	O
way	O
as	O
for	O
CSS	B-Language
,	O
though	O
some	O
of	O
the	O
rules	O
for	O
padding	O
and	O
margins	O
differ	O
between	O
FO	O
and	O
CSS	B-Language
.	O
</s>
<s>
The	O
language	O
of	O
the	O
FO	O
specification	O
,	O
unlike	O
that	O
of	O
CSS	B-Language
2.1	I-Language
,	O
uses	O
direction-neutral	O
terms	O
like	O
start	O
and	O
end	O
rather	O
than	O
left	O
and	O
right	O
when	O
describing	O
these	O
directions	O
.	O
</s>
<s>
XSL-FO	B-Language
'	O
s	O
basic	O
content	O
markup	O
is	O
derived	O
from	O
CSS	B-Language
and	O
its	O
cascading	O
rules	O
.	O
</s>
<s>
As	O
such	O
,	O
many	O
attributes	O
in	O
XSL-FO	B-Language
propagate	O
into	O
the	O
child	O
elements	O
unless	O
explicitly	O
overridden	O
.	O
</s>
<s>
XSL-FO	B-Language
is	O
capable	O
of	O
a	O
great	O
deal	O
of	O
textual	O
layout	O
functionality	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
information	O
as	O
specified	O
above	O
,	O
XSL-FO	B-Language
'	O
s	O
language	O
allows	O
for	O
the	O
specification	O
of	O
the	O
following	O
.	O
</s>
<s>
Because	O
of	O
the	O
nature	O
of	O
XSL-FO	B-Language
'	O
s	O
page	O
specification	O
,	O
multiple	O
pages	O
may	O
actually	O
have	O
different	O
numbers	O
and	O
widths	O
of	O
columns	O
.	O
</s>
<s>
An	O
XSL-FO	B-Language
list	O
is	O
,	O
essentially	O
,	O
two	O
sets	O
of	O
blocks	O
stacked	O
side	O
by	O
side	O
.	O
</s>
<s>
Numbering	O
of	O
XSL-FO	B-Language
lists	O
,	O
when	O
they	O
are	O
numbered	O
,	O
is	O
expected	O
to	O
be	O
done	O
by	O
the	O
XSLT	B-Application
,	O
or	O
whatever	O
other	O
process	O
,	O
that	O
generated	O
the	O
XSL-FO	B-Language
document	O
.	O
</s>
<s>
As	O
such	O
,	O
number	O
lists	O
are	O
to	O
be	O
explicitly	O
numbered	O
in	O
XSL-FO	B-Language
.	O
</s>
