<s>
The	O
identity	B-Algorithm
transform	I-Algorithm
is	O
a	O
data	B-General_Concept
transformation	I-General_Concept
that	O
copies	O
the	O
source	O
data	O
into	O
the	O
destination	O
data	O
without	O
change	O
.	O
</s>
<s>
By	O
creating	O
a	O
library	O
of	O
variations	O
of	O
the	O
base	O
identity	O
transformation	O
,	O
a	O
variety	O
of	O
data	B-General_Concept
transformation	I-General_Concept
filters	O
can	O
be	O
easily	O
maintained	O
.	O
</s>
<s>
These	O
filters	O
can	O
be	O
chained	O
together	O
in	O
a	O
format	O
similar	O
to	O
UNIX	B-Application
shell	O
pipes	O
.	O
</s>
<s>
The	O
most	O
frequently	O
cited	O
example	O
of	O
the	O
identity	B-Algorithm
transform	I-Algorithm
(	O
for	O
XSLT	B-Application
version	O
1.0	O
)	O
is	O
the	O
"	O
copy.xsl	O
"	O
transform	O
as	O
expressed	O
in	O
XSLT	B-Application
.	O
</s>
<s>
This	O
recursively	O
descends	O
the	O
element	O
tree	O
and	O
outputs	O
all	O
structures	O
in	O
the	O
same	O
structure	O
they	O
were	O
found	O
in	O
the	O
original	O
file	O
,	O
within	O
the	O
limitations	O
of	O
what	O
information	O
is	O
considered	O
significant	O
in	O
the	O
XPath	B-Application
data	I-Application
model	I-Application
.	O
</s>
<s>
A	O
more	O
explicit	O
version	O
of	O
the	O
identity	B-Algorithm
transform	I-Algorithm
is	O
:	O
</s>
<s>
XSLT	B-Application
3.0	O
specifies	O
an	O
on-no-match	O
attribute	O
of	O
the	O
xsl:mode	O
instruction	O
that	O
allows	O
the	O
identity	B-Algorithm
transform	I-Algorithm
to	O
be	O
declared	O
rather	O
than	O
implemented	O
as	O
an	O
explicit	O
template	O
rule	O
.	O
</s>
<s>
See	O
the	O
XSLT	B-Application
3.0	O
standard	O
's	O
description	O
of	O
shallow-copy	O
for	O
details	O
.	O
</s>
<s>
Finally	O
,	O
note	O
that	O
markup	O
details	O
,	O
such	O
as	O
the	O
use	O
of	O
CDATA	O
sections	O
or	O
the	O
order	O
of	O
attributes	O
,	O
are	O
not	O
necessarily	O
preserved	O
in	O
the	O
output	O
,	O
since	O
this	O
information	O
is	O
not	O
part	O
of	O
the	O
XPath	B-Application
data	I-Application
model	I-Application
.	O
</s>
<s>
To	O
show	O
CDATA	O
markup	O
in	O
the	O
output	O
,	O
the	O
XSLT	B-Application
stylesheet	O
that	O
contains	O
the	O
identity	B-Algorithm
transform	I-Algorithm
template	O
(	O
not	O
the	O
identity	B-Algorithm
transform	I-Algorithm
template	O
itself	O
)	O
should	O
make	O
use	O
of	O
the	O
xsl:output	O
attribute	O
called	O
cdata-section-elements	O
.	O
</s>
<s>
XQuery	B-Language
can	O
define	O
recursive	O
functions	O
.	O
</s>
<s>
The	O
following	O
example	O
XQuery	B-Language
function	O
copies	O
the	O
input	O
directly	O
to	O
the	O
output	O
without	O
modification	O
.	O
</s>
<s>
Here	O
one	O
important	O
note	O
about	O
the	O
XProc	B-Language
identity	O
,	O
is	O
that	O
it	O
can	O
take	O
either	O
one	O
document	O
like	O
this	O
example	O
or	O
a	O
sequence	O
of	O
document	O
as	O
input	O
.	O
</s>
<s>
Generally	O
the	O
identity	B-Algorithm
transform	I-Algorithm
is	O
used	O
as	O
a	O
base	O
on	O
which	O
one	O
can	O
make	O
local	O
modifications	O
.	O
</s>
