<s>
Extensible	B-Protocol
Markup	I-Protocol
Language	I-Protocol
(	O
XML	B-Protocol
)	O
is	O
a	O
markup	O
language	O
and	O
file	O
format	O
for	O
storing	O
,	O
transmitting	O
,	O
and	O
reconstructing	O
arbitrary	O
data	O
.	O
</s>
<s>
It	O
defines	O
a	O
set	O
of	O
rules	O
for	O
encoding	O
documents	O
in	O
a	O
format	O
that	O
is	O
both	O
human-readable	B-General_Concept
and	O
machine-readable	B-General_Concept
.	O
</s>
<s>
The	O
World	O
Wide	O
Web	O
Consortium	O
's	O
XML	B-Protocol
1.0	O
Specification	O
of	O
1998	O
and	O
several	O
other	O
related	O
specifications	O
—	O
all	O
of	O
them	O
free	O
open	O
standards	O
—	O
define	O
XML	B-Protocol
.	O
</s>
<s>
The	O
design	O
goals	O
of	O
XML	B-Protocol
emphasize	O
simplicity	O
,	O
generality	O
,	O
and	O
usability	O
across	O
the	O
Internet	O
.	O
</s>
<s>
Although	O
the	O
design	O
of	O
XML	B-Protocol
focuses	O
on	O
documents	O
,	O
the	O
language	O
is	O
widely	O
used	O
for	O
the	O
representation	O
of	O
arbitrary	O
data	B-General_Concept
structures	I-General_Concept
such	O
as	O
those	O
used	O
in	O
web	O
services	O
.	O
</s>
<s>
Several	O
schema	B-Language
systems	I-Language
exist	O
to	O
aid	O
in	O
the	O
definition	O
of	O
XML-based	B-Language
languages	I-Language
,	O
while	O
programmers	O
have	O
developed	O
many	O
application	B-Application
programming	I-Application
interfaces	I-Application
(	O
APIs	B-General_Concept
)	O
to	O
aid	O
the	O
processing	O
of	O
XML	B-Protocol
data	O
.	O
</s>
<s>
The	O
main	O
purpose	O
of	O
XML	B-Protocol
is	O
serialization	B-Application
,	O
i.e.	O
</s>
<s>
XML	B-Protocol
standardizes	O
this	O
process	O
.	O
</s>
<s>
As	O
a	O
markup	O
language	O
,	O
XML	B-Protocol
labels	O
,	O
categorizes	O
,	O
and	O
structurally	O
organizes	O
information	O
.	O
</s>
<s>
XML	B-Protocol
tags	O
represent	O
the	O
data	B-General_Concept
structure	I-General_Concept
and	O
contain	O
metadata	O
.	O
</s>
<s>
What	O
's	O
within	O
the	O
tags	O
is	O
data	O
,	O
encoded	O
in	O
the	O
way	O
the	O
XML	B-Protocol
standard	O
specifies	O
.	O
</s>
<s>
An	O
additional	O
XML	B-Language
schema	I-Language
(	O
XSD	O
)	O
defines	O
the	O
necessary	O
metadata	O
for	O
interpreting	O
and	O
validating	O
XML	B-Protocol
.	O
</s>
<s>
(	O
This	O
is	O
also	O
referred	O
to	O
as	O
the	O
canonical	O
schema	B-Language
.	O
)	O
</s>
<s>
An	O
XML	B-Protocol
document	I-Protocol
that	O
adheres	O
to	O
basic	O
XML	B-Protocol
rules	O
is	O
"	O
well-formed	B-General_Concept
"	O
;	O
one	O
that	O
adheres	O
to	O
its	O
schema	B-Language
is	O
"	O
valid.	O
"	O
</s>
<s>
IETF	O
RFC	O
7303	O
(	O
which	O
supersedes	O
the	O
older	O
RFC	O
3023	O
)	O
,	O
provides	O
rules	O
for	O
the	O
construction	O
of	O
media	B-Application
types	I-Application
for	O
use	O
in	O
XML	B-Protocol
message	O
.	O
</s>
<s>
It	O
defines	O
three	O
media	B-Application
types	I-Application
:	O
application/xml	O
(	O
text/xml	B-Protocol
is	O
an	O
alias	O
)	O
,	O
application/xml	O
-external-parsed-entity	O
(	O
text/xml	B-Protocol
-external-parsed-entity	O
is	O
an	O
alias	O
)	O
and	O
application/xml	O
-dtd	O
.	O
</s>
<s>
They	O
are	O
used	O
for	O
transmitting	O
raw	O
XML	B-Protocol
files	O
without	O
exposing	O
their	O
internal	O
semantics	B-Application
.	O
</s>
<s>
RFC	O
7303	O
further	O
recommends	O
that	O
XML-based	B-Language
languages	I-Language
be	O
given	O
media	B-Application
types	I-Application
ending	O
in	O
+xml	O
,	O
for	O
example	O
,	O
image/svg	O
+xml	O
for	O
SVG	B-Application
.	O
</s>
<s>
Further	O
guidelines	O
for	O
the	O
use	O
of	O
XML	B-Protocol
in	O
a	O
networked	O
context	O
appear	O
in	O
RFC	O
3470	O
,	O
also	O
known	O
as	O
IETF	O
BCP	O
70	O
,	O
a	O
document	B-Protocol
covering	O
many	O
aspects	O
of	O
designing	O
and	O
deploying	O
an	O
XML-based	O
language	O
.	O
</s>
<s>
XML	B-Protocol
has	O
come	O
into	O
common	O
use	O
for	O
the	O
interchange	O
of	O
data	O
over	O
the	O
Internet	O
.	O
</s>
<s>
Hundreds	O
of	O
document	B-Protocol
formats	O
using	O
XML	B-Protocol
syntax	O
have	O
been	O
developed	O
,	O
including	O
RSS	O
,	O
Atom	B-Application
,	O
Office	B-Operating_System
Open	I-Operating_System
XML	I-Operating_System
,	O
OpenDocument	B-Application
,	O
SVG	B-Application
,	O
and	O
XHTML	B-Language
.	O
</s>
<s>
XML	B-Protocol
also	O
provides	O
the	O
base	O
language	O
for	O
communication	O
protocols	O
such	O
as	O
SOAP	B-Application
and	O
XMPP	B-Protocol
.	O
</s>
<s>
It	O
is	O
the	O
message	O
exchange	O
format	O
for	O
the	O
Asynchronous	B-General_Concept
JavaScript	I-General_Concept
and	I-General_Concept
XML	I-General_Concept
(	O
AJAX	B-General_Concept
)	O
programming	O
technique	O
.	O
</s>
<s>
Many	O
industry	O
data	O
standards	O
,	O
such	O
as	O
Health	O
Level	O
7	O
,	O
OpenTravel	O
Alliance	O
,	O
FpML	B-Application
,	O
MISMO	O
,	O
and	O
National	O
Information	O
Exchange	O
Model	O
are	O
based	O
on	O
XML	B-Protocol
and	O
the	O
rich	O
features	B-Architecture
of	O
the	O
XML	B-Language
schema	I-Language
specification	O
.	O
</s>
<s>
In	O
publishing	O
,	O
Darwin	B-Language
Information	I-Language
Typing	I-Language
Architecture	I-Language
is	O
an	O
XML	B-Protocol
industry	O
data	O
standard	O
.	O
</s>
<s>
XML	B-Protocol
is	O
used	O
extensively	O
to	O
underpin	O
various	O
publishing	O
formats	O
.	O
</s>
<s>
The	O
material	O
in	O
this	O
section	O
is	O
based	O
on	O
the	O
XML	B-Protocol
Specification	I-Protocol
.	O
</s>
<s>
This	O
is	O
not	O
an	O
exhaustive	O
list	O
of	O
all	O
the	O
constructs	O
that	O
appear	O
in	O
XML	B-Protocol
;	O
it	O
provides	O
an	O
introduction	O
to	O
the	O
key	O
constructs	O
most	O
often	O
encountered	O
in	O
day-to-day	O
use	O
.	O
</s>
<s>
An	O
XML	B-Protocol
document	I-Protocol
is	O
a	O
string	O
of	O
characters	O
.	O
</s>
<s>
Every	O
legal	O
Unicode	O
character	O
(	O
except	O
Null	O
)	O
may	O
appear	O
in	O
an	O
(	O
1.1	O
)	O
XML	B-Protocol
document	I-Protocol
(	O
while	O
some	O
are	O
discouraged	O
)	O
.	O
</s>
<s>
The	O
specification	O
places	O
requirements	O
on	O
what	O
an	O
XML	B-Protocol
processor	O
must	O
do	O
and	O
not	O
do	O
,	O
but	O
the	O
application	O
is	O
outside	O
its	O
scope	O
.	O
</s>
<s>
The	O
processor	O
(	O
as	O
the	O
specification	O
calls	O
it	O
)	O
is	O
often	O
referred	O
to	O
colloquially	O
as	O
an	O
XML	B-Protocol
parser	I-Protocol
.	O
</s>
<s>
The	O
characters	O
making	O
up	O
an	O
XML	B-Protocol
document	I-Protocol
are	O
divided	O
into	O
markup	O
and	O
content	O
,	O
which	O
may	O
be	O
distinguished	O
by	O
the	O
application	O
of	O
simple	O
syntactic	O
rules	O
.	O
</s>
<s>
However	O
,	O
in	O
a	O
CDATA	B-Language
section	I-Language
,	O
the	O
delimiters	O
<	O
!	O
</s>
<s>
[	O
CDATA[ 	O
and	O
 ] ]	O
>	O
are	O
classified	O
as	O
markup	O
,	O
while	O
the	O
text	O
between	O
them	O
is	O
classified	O
as	O
content	O
.	O
</s>
<s>
An	O
element	O
is	O
a	O
logical	O
document	B-Protocol
component	O
that	O
either	O
begins	O
with	O
a	O
start-tag	O
and	O
ends	O
with	O
a	O
matching	O
end-tag	O
or	O
consists	O
only	O
of	O
an	O
empty-element	O
tag	O
.	O
</s>
<s>
An	O
attribute	O
is	O
a	O
markup	O
construct	O
consisting	O
of	O
a	O
name	B-Application
–	I-Application
value	I-Application
pair	I-Application
that	O
exists	O
within	O
a	O
start-tag	O
or	O
empty-element	O
tag	O
.	O
</s>
<s>
An	O
XML	B-Protocol
attribute	O
can	O
only	O
have	O
a	O
single	O
value	O
and	O
each	O
attribute	O
can	O
appear	O
at	O
most	O
once	O
on	O
each	O
element	O
.	O
</s>
<s>
In	O
the	O
common	O
situation	O
where	O
a	O
list	O
of	O
multiple	O
values	O
is	O
desired	O
,	O
this	O
must	O
be	O
done	O
by	O
encoding	O
the	O
list	O
into	O
a	O
well-formed	B-Language
XML	I-Language
attribute	O
with	O
some	O
format	O
beyond	O
what	O
XML	B-Protocol
defines	O
itself	O
.	O
</s>
<s>
<div class="inner greeting-box">Welcome!</div>	O
,	O
where	O
the	O
attribute	O
"	O
class	O
"	O
has	O
both	O
the	O
value	O
"	O
inner	O
greeting-box	O
"	O
and	O
also	O
indicates	O
the	O
two	O
CSS	B-Language
class	O
names	O
"	O
inner	O
"	O
and	O
"	O
greeting-box	O
"	O
.	O
</s>
<s>
XML	B-Protocol
documents	I-Protocol
may	O
begin	O
with	O
an	O
XML	B-Protocol
declaration	O
that	O
describes	O
some	O
information	O
about	O
themselves	O
.	O
</s>
<s>
An	O
example	O
is	O
<?xml version="1.0" encoding="UTF-8"?>	O
.	O
</s>
<s>
XML	B-Protocol
documents	I-Protocol
consist	O
entirely	O
of	O
characters	O
from	O
the	O
Unicode	O
repertoire	O
.	O
</s>
<s>
Except	O
for	O
a	O
small	O
number	O
of	O
specifically	O
excluded	O
control	O
characters	O
,	O
any	O
character	O
defined	O
by	O
Unicode	O
may	O
appear	O
within	O
the	O
content	O
of	O
an	O
XML	B-Protocol
document	I-Protocol
.	O
</s>
<s>
XML	B-Protocol
includes	O
facilities	O
for	O
identifying	O
the	O
encoding	O
of	O
the	O
Unicode	O
characters	O
that	O
make	O
up	O
the	O
document	B-Protocol
,	O
and	O
for	O
expressing	O
characters	O
that	O
,	O
for	O
one	O
reason	O
or	O
another	O
,	O
cannot	O
be	O
used	O
directly	O
.	O
</s>
<s>
Unicode	O
code	O
points	O
in	O
the	O
following	O
ranges	O
are	O
valid	O
in	O
XML	B-Protocol
1.0	O
documents	O
:	O
</s>
<s>
U+0009	O
(	O
Horizontal	O
Tab	O
)	O
,	O
U+000A	O
(	O
Line	O
Feed	O
)	O
,	O
U+000D	O
(	O
Carriage	O
Return	O
)	O
:	O
these	O
are	O
the	O
only	O
C0	O
controls	O
accepted	O
in	O
XML	B-Protocol
1.0	O
;	O
</s>
<s>
XML	B-Protocol
1.1	O
extends	O
the	O
set	O
of	O
allowed	O
characters	O
to	O
include	O
all	O
the	O
above	O
,	O
plus	O
the	O
remaining	O
characters	O
in	O
the	O
range	O
U+0001	O
–	O
U+001F	O
.	O
</s>
<s>
The	O
code	O
point	O
U+0000	O
(	O
Null	O
)	O
is	O
the	O
only	O
character	O
that	O
is	O
not	O
permitted	O
in	O
any	O
XML	B-Protocol
1.1	O
document	B-Protocol
.	O
</s>
<s>
The	O
Unicode	O
character	B-General_Concept
set	I-General_Concept
can	O
be	O
encoded	O
into	O
bytes	O
for	O
storage	O
or	O
transmission	O
in	O
a	O
variety	O
of	O
different	O
ways	O
,	O
called	O
"	O
encodings	O
"	O
.	O
</s>
<s>
Unicode	O
itself	O
defines	O
encodings	O
that	O
cover	O
the	O
entire	O
repertoire	O
;	O
well-known	O
ones	O
include	O
UTF-8	O
(	O
which	O
the	O
XML	B-Protocol
standard	O
recommends	O
using	O
,	O
without	O
a	O
BOM	O
)	O
and	O
UTF-16	O
.	O
</s>
<s>
There	O
are	O
many	O
other	O
text	B-General_Concept
encodings	I-General_Concept
that	O
predate	O
Unicode	O
,	O
such	O
as	O
ASCII	B-Protocol
and	O
various	O
ISO/IEC	O
8859	O
;	O
their	O
character	O
repertoires	O
are	O
in	O
every	O
case	O
subsets	O
of	O
the	O
Unicode	O
character	B-General_Concept
set	I-General_Concept
.	O
</s>
<s>
XML	B-Protocol
allows	O
the	O
use	O
of	O
any	O
of	O
the	O
Unicode-defined	O
encodings	O
and	O
any	O
other	O
encodings	O
whose	O
characters	O
also	O
appear	O
in	O
Unicode	O
.	O
</s>
<s>
XML	B-Protocol
also	O
provides	O
a	O
mechanism	O
whereby	O
an	O
XML	B-Protocol
processor	O
can	O
reliably	O
,	O
without	O
any	O
prior	O
knowledge	O
,	O
determine	O
which	O
encoding	O
is	O
being	O
used	O
.	O
</s>
<s>
Encodings	O
other	O
than	O
UTF-8	O
and	O
UTF-16	O
are	O
not	O
necessarily	O
recognized	O
by	O
every	O
XML	B-Protocol
parser	I-Protocol
(	O
and	O
in	O
some	O
cases	O
not	O
even	O
UTF-16	O
,	O
even	O
though	O
the	O
standard	O
mandates	O
it	O
to	O
also	O
be	O
recognized	O
)	O
.	O
</s>
<s>
XML	B-Protocol
provides	O
escape	O
facilities	O
for	O
including	O
characters	O
that	O
are	O
problematic	O
to	O
include	O
directly	O
.	O
</s>
<s>
The	O
characters	O
""	O
and	O
""	O
are	O
key	O
syntax	O
markers	O
and	O
may	O
never	O
appear	O
in	O
content	O
outside	O
a	O
CDATA	B-Language
section	I-Language
.	O
</s>
<s>
It	O
is	O
allowed	O
,	O
but	O
not	O
recommended	O
,	O
to	O
use	O
""	O
in	O
XML	B-Language
entity	I-Language
values	O
.	O
</s>
<s>
Some	O
character	B-General_Concept
encodings	I-General_Concept
support	O
only	O
a	O
subset	O
of	O
Unicode	O
.	O
</s>
<s>
For	O
example	O
,	O
it	O
is	O
legal	O
to	O
encode	O
an	O
XML	B-Protocol
document	I-Protocol
in	O
ASCII	B-Protocol
,	O
but	O
ASCII	B-Protocol
lacks	O
code	O
points	O
for	O
Unicode	O
characters	O
such	O
as	O
"	O
é	O
"	O
.	O
</s>
<s>
All	O
permitted	O
Unicode	O
characters	O
may	O
be	O
represented	O
with	O
a	O
numeric	B-General_Concept
character	I-General_Concept
reference	I-General_Concept
.	O
</s>
<s>
A	O
user	O
whose	O
keyboard	O
offers	O
no	O
method	O
for	O
entering	O
this	O
character	O
could	O
still	O
insert	O
it	O
in	O
an	O
XML	B-Protocol
document	I-Protocol
encoded	O
either	O
as	O
中	O
or	O
中	O
.	O
</s>
<s>
Similarly	O
,	O
the	O
string	O
"	O
I	O
3	O
Jörg	O
"	O
could	O
be	O
encoded	O
for	O
inclusion	O
in	O
an	O
XML	B-Protocol
document	I-Protocol
as	O
I	O
<3	O
Jörg	O
.	O
</s>
<s>
�	O
is	O
not	O
permitted	O
because	O
the	O
null	O
character	O
is	O
one	O
of	O
the	O
control	O
characters	O
excluded	O
from	O
XML	B-Protocol
,	O
even	O
when	O
using	O
a	O
numeric	B-General_Concept
character	I-General_Concept
reference	I-General_Concept
.	O
</s>
<s>
An	O
alternative	O
encoding	O
mechanism	O
such	O
as	O
Base64	B-Protocol
is	O
needed	O
to	O
represent	O
such	O
characters	O
.	O
</s>
<s>
Comments	O
may	O
appear	O
anywhere	O
in	O
a	O
document	B-Protocol
outside	O
other	O
markup	O
.	O
</s>
<s>
Comments	O
cannot	O
appear	O
before	O
the	O
XML	B-Protocol
declaration	O
.	O
</s>
<s>
For	O
compatibility	O
with	O
SGML	B-Language
,	O
the	O
string	O
"	O
--	O
 "	O
(	O
double-hyphen	O
)	O
is	O
not	O
allowed	O
inside	O
comments	O
;	O
this	O
means	O
comments	O
cannot	O
be	O
nested	O
.	O
</s>
<s>
The	O
ampersand	O
has	O
no	O
special	O
significance	O
within	O
comments	O
,	O
so	O
entity	O
and	O
character	O
references	O
are	O
not	O
recognized	O
as	O
such	O
,	O
and	O
there	O
is	O
no	O
way	O
to	O
represent	O
characters	O
outside	O
the	O
character	B-General_Concept
set	I-General_Concept
of	O
the	O
document	B-Protocol
encoding	O
.	O
</s>
<s>
XML	B-Protocol
1.0	O
(	O
Fifth	O
Edition	O
)	O
and	O
XML	B-Protocol
1.1	O
support	O
the	O
direct	O
use	O
of	O
almost	O
any	O
Unicode	O
character	O
in	O
element	O
names	O
,	O
attributes	O
,	O
comments	O
,	O
character	B-Language
data	I-Language
,	O
and	O
processing	B-Language
instructions	I-Language
(	O
other	O
than	O
the	O
ones	O
that	O
have	O
special	O
symbolic	O
meaning	O
in	O
XML	B-Protocol
itself	O
,	O
such	O
as	O
the	O
less-than	O
sign	O
,	O
"	O
<	O
"	O
)	O
.	O
</s>
<s>
The	O
following	O
is	O
a	O
well-formed	B-Language
XML	I-Language
document	I-Language
including	O
Chinese	O
,	O
Armenian	O
and	O
Cyrillic	O
characters	O
:	O
</s>
<s>
The	O
XML	B-Protocol
specification	I-Protocol
defines	O
an	O
XML	B-Protocol
document	I-Protocol
as	O
a	O
well-formed	B-General_Concept
text	O
,	O
meaning	O
that	O
it	O
satisfies	O
a	O
list	O
of	O
syntax	O
rules	O
provided	O
in	O
the	O
specification	O
.	O
</s>
<s>
The	O
document	B-Protocol
contains	O
only	O
properly	O
encoded	O
legal	O
Unicode	O
characters	O
.	O
</s>
<s>
The	O
start-tag	O
,	O
end-tag	O
,	O
and	O
empty-element	O
tag	O
that	O
delimit	O
elements	O
are	O
correctly	O
nested	O
,	O
with	O
none	B-Language
missing	I-Language
and	O
none	O
overlapping	O
.	O
</s>
<s>
The	O
definition	O
of	O
an	O
XML	B-Protocol
document	I-Protocol
excludes	O
texts	O
that	O
contain	O
violations	O
of	O
well-formedness	O
rules	O
;	O
they	O
are	O
simply	O
not	O
XML	B-Protocol
.	O
</s>
<s>
An	O
XML	B-Protocol
processor	O
that	O
encounters	O
such	O
a	O
violation	O
is	O
required	O
to	O
report	O
such	O
errors	O
and	O
to	O
cease	O
normal	O
processing	O
.	O
</s>
<s>
This	O
policy	O
,	O
occasionally	O
referred	O
to	O
as	O
"	O
draconian	O
error	O
handling	O
,	O
"	O
stands	O
in	O
notable	O
contrast	O
to	O
the	O
behavior	O
of	O
programs	O
that	O
process	O
HTML	B-Language
,	O
which	O
are	O
designed	O
to	O
produce	O
a	O
reasonable	O
result	O
even	O
in	O
the	O
presence	O
of	O
severe	O
markup	O
errors	O
.	O
</s>
<s>
XML	B-Protocol
's	O
policy	O
in	O
this	O
area	O
has	O
been	O
criticized	O
as	O
a	O
violation	O
of	O
Postel	O
's	O
law	O
(	O
"	O
Be	O
conservative	O
in	O
what	O
you	O
send	O
;	O
be	O
liberal	O
in	O
what	O
you	O
accept	O
"	O
)	O
.	O
</s>
<s>
The	O
XML	B-Protocol
specification	I-Protocol
defines	O
a	O
valid	B-Language
XML	I-Language
document	I-Language
as	O
a	O
well-formed	B-Language
XML	I-Language
document	I-Language
which	O
also	O
conforms	O
to	O
the	O
rules	O
of	O
a	O
Document	B-Language
Type	I-Language
Definition	I-Language
(	O
DTD	O
)	O
.	O
</s>
<s>
In	O
addition	O
to	O
being	O
well	O
formed	O
,	O
an	O
XML	B-Protocol
document	I-Protocol
may	O
be	O
valid	O
.	O
</s>
<s>
This	O
means	O
that	O
it	O
contains	O
a	O
reference	O
to	O
a	O
Document	B-Language
Type	I-Language
Definition	I-Language
(	O
DTD	O
)	O
,	O
and	O
that	O
its	O
elements	O
and	O
attributes	O
are	O
declared	O
in	O
that	O
DTD	O
and	O
follow	O
the	O
grammatical	O
rules	O
for	O
them	O
that	O
the	O
DTD	O
specifies	O
.	O
</s>
<s>
XML	B-Protocol
processors	O
are	O
classified	O
as	O
validating	O
or	O
non-validating	O
depending	O
on	O
whether	O
or	O
not	O
they	O
check	O
XML	B-Protocol
documents	I-Protocol
for	O
validity	O
.	O
</s>
<s>
A	O
DTD	O
is	O
an	O
example	O
of	O
a	O
schema	B-Language
or	O
grammar	O
.	O
</s>
<s>
Since	O
the	O
initial	O
publication	O
of	O
XML	B-Protocol
1.0	O
,	O
there	O
has	O
been	O
substantial	O
work	O
in	O
the	O
area	O
of	O
schema	B-Language
languages	O
for	O
XML	B-Protocol
.	O
</s>
<s>
Such	O
schema	B-Language
languages	O
typically	O
constrain	O
the	O
set	O
of	O
elements	O
that	O
may	O
be	O
used	O
in	O
a	O
document	B-Protocol
,	O
which	O
attributes	O
may	O
be	O
applied	O
to	O
them	O
,	O
the	O
order	O
in	O
which	O
they	O
may	O
appear	O
,	O
and	O
the	O
allowable	O
parent/child	O
relationships	O
.	O
</s>
<s>
The	O
oldest	O
schema	B-Language
language	O
for	O
XML	B-Protocol
is	O
the	O
document	B-Language
type	I-Language
definition	I-Language
(	O
DTD	O
)	O
,	O
inherited	O
from	O
SGML	B-Language
.	O
</s>
<s>
DTD	O
support	O
is	O
ubiquitous	O
due	O
to	O
its	O
inclusion	O
in	O
the	O
XML	B-Protocol
1.0	O
standard	O
.	O
</s>
<s>
DTDs	O
are	O
terse	O
compared	O
to	O
element-based	O
schema	B-Language
languages	O
and	O
consequently	O
present	O
more	O
information	O
in	O
a	O
single	O
screen	O
.	O
</s>
<s>
DTDs	O
allow	O
the	O
declaration	O
of	O
standard	B-Language
public	I-Language
entity	I-Language
sets	I-Language
for	O
publishing	O
characters	O
.	O
</s>
<s>
DTDs	O
define	O
a	O
document	B-Protocol
type	O
rather	O
than	O
the	O
types	O
used	O
by	O
a	O
namespace	B-Language
,	O
thus	O
grouping	O
all	O
constraints	O
for	O
a	O
document	B-Protocol
in	O
a	O
single	O
collection	O
.	O
</s>
<s>
They	O
have	O
no	O
explicit	O
support	O
for	O
newer	O
features	B-Architecture
of	O
XML	B-Protocol
,	O
most	O
importantly	O
namespaces	B-Language
.	O
</s>
<s>
XML	B-Language
DTDs	I-Language
are	O
simpler	O
than	O
SGML	B-Language
DTDs	O
and	O
there	O
are	O
certain	O
structures	O
that	O
cannot	O
be	O
expressed	O
with	O
regular	O
grammars	O
.	O
</s>
<s>
They	O
use	O
a	O
syntax	O
based	O
on	O
regular	B-Language
expression	I-Language
syntax	O
,	O
inherited	O
from	O
SGML	B-Language
,	O
to	O
describe	O
the	O
schema	B-Language
.	O
</s>
<s>
Typical	O
XML	B-Protocol
APIs	B-General_Concept
such	O
as	O
SAX	B-Application
do	O
not	O
attempt	O
to	O
offer	O
applications	O
a	O
structured	O
representation	O
of	O
the	O
syntax	O
,	O
so	O
it	O
is	O
less	O
accessible	O
to	O
programmers	O
than	O
an	O
element-based	O
syntax	O
may	O
be	O
.	O
</s>
<s>
Two	O
peculiar	O
features	B-Architecture
that	O
distinguish	O
DTDs	O
from	O
other	O
schema	B-Language
types	O
are	O
the	O
syntactic	O
support	O
for	O
embedding	O
a	O
DTD	O
within	O
XML	B-Protocol
documents	I-Protocol
and	O
for	O
defining	O
entities	O
,	O
which	O
are	O
arbitrary	O
fragments	O
of	O
text	O
or	O
markup	O
that	O
the	O
XML	B-Protocol
processor	O
inserts	O
in	O
the	O
DTD	O
itself	O
and	O
in	O
the	O
XML	B-Protocol
document	I-Protocol
wherever	O
they	O
are	O
referenced	O
,	O
like	O
character	O
escapes	O
.	O
</s>
<s>
A	O
newer	O
schema	B-Language
language	O
,	O
described	O
by	O
the	O
W3C	O
as	O
the	O
successor	O
of	O
DTDs	O
,	O
is	O
XML	B-Language
Schema	I-Language
,	O
often	O
referred	O
to	O
by	O
the	O
initialism	O
for	O
XML	B-Language
Schema	I-Language
instances	O
,	O
XSD	O
(	O
XML	B-Language
Schema	I-Language
Definition	O
)	O
.	O
</s>
<s>
XSDs	O
are	O
far	O
more	O
powerful	O
than	O
DTDs	O
in	O
describing	O
XML	B-Language
languages	I-Language
.	O
</s>
<s>
They	O
use	O
a	O
rich	O
datatyping	O
system	O
and	O
allow	O
for	O
more	O
detailed	O
constraints	O
on	O
an	O
XML	B-Protocol
document	I-Protocol
's	O
logical	O
structure	O
.	O
</s>
<s>
XSDs	O
also	O
use	O
an	O
XML-based	O
format	O
,	O
which	O
makes	O
it	O
possible	O
to	O
use	O
ordinary	O
XML	B-Protocol
tools	O
to	O
help	O
process	O
them	O
.	O
</s>
<s>
xs:schema	O
element	O
that	O
defines	O
a	O
schema	B-Language
:	O
</s>
<s>
RELAX	B-Language
NG	I-Language
(	O
Regular	O
Language	O
for	O
XML	B-Protocol
Next	O
Generation	O
)	O
was	O
initially	O
specified	O
by	O
OASIS	O
and	O
is	O
now	O
a	O
standard	O
(	O
Part	O
2	O
:	O
Regular-grammar-based	O
validation	O
of	O
ISO/IEC	B-Language
19757	I-Language
–	I-Language
DSDL	I-Language
)	O
.	O
</s>
<s>
RELAX	B-Language
NG	I-Language
schemas	O
may	O
be	O
written	O
in	O
either	O
an	O
XML	B-Protocol
based	O
syntax	O
or	O
a	O
more	O
compact	O
non-XML	O
syntax	O
;	O
the	O
two	O
syntaxes	O
are	O
isomorphic	O
and	O
James	O
Clark	O
's	O
conversion	O
tool	O
—	O
—	O
can	O
convert	O
between	O
them	O
without	O
loss	O
of	O
information	O
.	O
</s>
<s>
RELAX	B-Language
NG	I-Language
has	O
a	O
simpler	O
definition	O
and	O
validation	O
framework	O
than	O
XML	B-Language
Schema	I-Language
,	O
making	O
it	O
easier	O
to	O
use	O
and	O
implement	O
.	O
</s>
<s>
It	O
also	O
has	O
the	O
ability	O
to	O
use	O
datatype	O
framework	O
plug-ins	B-Application
;	O
a	O
RELAX	B-Language
NG	I-Language
schema	B-Language
author	O
,	O
for	O
example	O
,	O
can	O
require	O
values	O
in	O
an	O
XML	B-Protocol
document	I-Protocol
to	O
conform	O
to	O
definitions	O
in	O
XML	B-Language
Schema	I-Language
Datatypes	O
.	O
</s>
<s>
Schematron	B-Language
is	O
a	O
language	O
for	O
making	O
assertions	O
about	O
the	O
presence	O
or	O
absence	O
of	O
patterns	O
in	O
an	O
XML	B-Protocol
document	I-Protocol
.	O
</s>
<s>
It	O
typically	O
uses	O
XPath	B-Language
expressions	O
.	O
</s>
<s>
Schematron	B-Language
is	O
now	O
a	O
standard	O
(	O
Part	O
3	O
:	O
Rule-based	O
validation	O
of	O
ISO/IEC	B-Language
19757	I-Language
–	I-Language
DSDL	I-Language
)	O
.	O
</s>
<s>
DSDL	B-Language
(	O
Document	B-Language
Schema	I-Language
Definition	I-Language
Languages	I-Language
)	O
is	O
a	O
multi-part	O
ISO/IEC	O
standard	O
(	O
ISO/IEC	B-Language
19757	I-Language
)	O
that	O
brings	O
together	O
a	O
comprehensive	O
set	O
of	O
small	O
schema	B-Language
languages	O
,	O
each	O
targeted	O
at	O
specific	O
problems	O
.	O
</s>
<s>
DSDL	B-Language
includes	O
RELAX	B-Language
NG	I-Language
full	O
and	O
compact	O
syntax	O
,	O
Schematron	B-Language
assertion	O
language	O
,	O
and	O
languages	O
for	O
defining	O
datatypes	O
,	O
character	O
repertoire	O
constraints	O
,	O
renaming	O
and	O
entity	O
expansion	O
,	O
and	O
namespace-based	O
routing	B-Protocol
of	O
document	B-Protocol
fragments	O
to	O
different	O
validators	O
.	O
</s>
<s>
DSDL	B-Language
schema	B-Language
languages	O
do	O
not	O
have	O
the	O
vendor	O
support	O
of	O
XML	B-Language
Schemas	I-Language
yet	O
,	O
and	O
are	O
to	O
some	O
extent	O
a	O
grassroots	O
reaction	O
of	O
industrial	O
publishers	O
to	O
the	O
lack	O
of	O
utility	O
of	O
XML	B-Language
Schemas	I-Language
for	O
publishing	O
.	O
</s>
<s>
Some	O
schema	B-Language
languages	O
not	O
only	O
describe	O
the	O
structure	O
of	O
a	O
particular	O
XML	B-Protocol
format	O
but	O
also	O
offer	O
limited	O
facilities	O
to	O
influence	O
processing	O
of	O
individual	O
XML	B-Protocol
files	O
that	O
conform	O
to	O
this	O
format	O
.	O
</s>
<s>
RELAX	B-Language
NG	I-Language
and	O
Schematron	B-Language
intentionally	O
do	O
not	O
provide	O
these	O
.	O
</s>
<s>
A	O
cluster	O
of	O
specifications	O
closely	O
related	O
to	O
XML	B-Protocol
have	O
been	O
developed	O
,	O
starting	O
soon	O
after	O
the	O
initial	O
publication	O
of	O
XML	B-Protocol
1.0	O
.	O
</s>
<s>
It	O
is	O
frequently	O
the	O
case	O
that	O
the	O
term	O
"	O
XML	B-Protocol
"	O
is	O
used	O
to	O
refer	O
to	O
XML	B-Protocol
together	O
with	O
one	O
or	O
more	O
of	O
these	O
other	O
technologies	O
that	O
have	O
come	O
to	O
be	O
seen	O
as	O
part	O
of	O
the	O
XML	B-Protocol
core	O
.	O
</s>
<s>
XML	B-Language
namespaces	I-Language
enable	O
the	O
same	O
document	B-Protocol
to	O
contain	O
XML	B-Protocol
elements	O
and	O
attributes	O
taken	O
from	O
different	O
vocabularies	O
,	O
without	O
any	O
naming	O
collisions	O
occurring	O
.	O
</s>
<s>
Although	O
XML	B-Language
Namespaces	I-Language
are	O
not	O
part	O
of	O
the	O
XML	B-Protocol
specification	I-Protocol
itself	O
,	O
virtually	O
all	O
XML	B-Protocol
software	O
also	O
supports	O
XML	B-Language
Namespaces	I-Language
.	O
</s>
<s>
XML	B-Protocol
Base	O
defines	O
the	O
xml:base	O
attribute	O
,	O
which	O
may	O
be	O
used	O
to	O
set	O
the	O
base	O
for	O
resolution	O
of	O
relative	O
URI	O
references	O
within	O
the	O
scope	O
of	O
a	O
single	O
XML	B-Protocol
element	O
.	O
</s>
<s>
XML	B-Protocol
Information	O
Set	O
or	O
XML	B-Protocol
Infoset	O
is	O
an	O
abstract	O
data	O
model	O
for	O
XML	B-Protocol
documents	I-Protocol
in	O
terms	O
of	O
information	O
items	O
.	O
</s>
<s>
The	O
infoset	O
is	O
commonly	O
used	O
in	O
the	O
specifications	O
of	O
XML	B-Language
languages	I-Language
,	O
for	O
convenience	O
in	O
describing	O
constraints	O
on	O
the	O
XML	B-Protocol
constructs	O
those	O
languages	O
allow	O
.	O
</s>
<s>
XSL	B-Language
(	O
Extensible	B-Language
Stylesheet	I-Language
Language	I-Language
)	O
is	O
a	O
family	O
of	O
languages	O
used	O
to	O
transform	O
and	O
render	O
XML	B-Protocol
documents	I-Protocol
,	O
split	O
into	O
three	O
parts	O
:	O
</s>
<s>
XSLT	B-Application
(	O
XSL	B-Application
Transformations	I-Application
)	O
,	O
an	O
XML	B-Protocol
language	O
for	O
transforming	O
XML	B-Protocol
documents	I-Protocol
into	O
other	O
XML	B-Protocol
documents	I-Protocol
or	O
other	O
formats	O
such	O
as	O
HTML	B-Language
,	O
plain	O
text	O
,	O
or	O
XSL-FO	B-Language
.	O
</s>
<s>
XSLT	B-Application
is	O
very	O
tightly	O
coupled	O
with	O
XPath	B-Language
,	O
which	O
it	O
uses	O
to	O
address	O
components	O
of	O
the	O
input	O
XML	B-Protocol
document	I-Protocol
,	O
mainly	O
elements	O
and	O
attributes	O
.	O
</s>
<s>
XSL-FO	B-Language
(	O
XSL	B-Language
Formatting	I-Language
Objects	I-Language
)	O
,	O
an	O
XML	B-Protocol
language	O
for	O
rendering	O
XML	B-Protocol
documents	I-Protocol
,	O
often	O
used	O
to	O
generate	O
PDFs	O
.	O
</s>
<s>
XPath	B-Language
(	O
XML	B-Language
Path	I-Language
Language	I-Language
)	O
,	O
a	O
non-XML	O
language	O
for	O
addressing	O
the	O
components	O
(	O
elements	O
,	O
attributes	O
,	O
and	O
so	O
on	O
)	O
of	O
an	O
XML	B-Protocol
document	I-Protocol
.	O
</s>
<s>
XPath	B-Language
is	O
widely	O
used	O
in	O
other	O
core-XML	O
specifications	O
and	O
in	O
programming	O
libraries	O
for	O
accessing	O
XML-encoded	O
data	O
.	O
</s>
<s>
XQuery	B-Language
(	O
XML	B-Protocol
Query	O
)	O
is	O
an	O
XML	B-Language
query	I-Language
language	I-Language
strongly	O
rooted	O
in	O
XPath	B-Language
and	O
XML	B-Language
Schema	I-Language
.	O
</s>
<s>
It	O
provides	O
methods	B-Language
to	O
access	O
,	O
manipulate	O
and	O
return	O
XML	B-Protocol
,	O
and	O
is	O
mainly	O
conceived	O
as	O
a	O
query	O
language	O
for	O
XML	B-Application
databases	I-Application
.	O
</s>
<s>
XML	B-Protocol
Signature	O
defines	O
syntax	O
and	O
processing	O
rules	O
for	O
creating	O
digital	O
signatures	O
on	O
XML	B-Protocol
content	O
.	O
</s>
<s>
XML	B-Protocol
Encryption	O
defines	O
syntax	O
and	O
processing	O
rules	O
for	O
encrypting	O
XML	B-Protocol
content	O
.	O
</s>
<s>
XML	B-Protocol
model	O
(	O
Part	O
11	O
:	O
Schema	B-Language
Association	O
of	O
ISO/IEC	B-Language
19757	I-Language
–	I-Language
DSDL	I-Language
)	O
defines	O
a	O
means	O
of	O
associating	O
any	O
xml	B-Protocol
document	I-Protocol
with	O
any	O
of	O
the	O
schema	B-Language
types	O
mentioned	O
above	O
.	O
</s>
<s>
Some	O
other	O
specifications	O
conceived	O
as	O
part	O
of	O
the	O
"	O
XML	B-Protocol
Core	O
"	O
have	O
failed	O
to	O
find	O
wide	O
adoption	O
,	O
including	O
XInclude	O
,	O
XLink	O
,	O
and	O
XPointer	B-General_Concept
.	O
</s>
<s>
The	O
design	O
goals	O
of	O
XML	B-Protocol
include	O
,	O
"	O
It	O
shall	O
be	O
easy	O
to	O
write	O
programs	O
which	O
process	O
XML	B-Protocol
documents.	O
"	O
</s>
<s>
Despite	O
this	O
,	O
the	O
XML	B-Protocol
specification	I-Protocol
contains	O
almost	O
no	O
information	O
about	O
how	O
programmers	O
might	O
go	O
about	O
doing	O
such	O
processing	O
.	O
</s>
<s>
The	O
XML	B-Protocol
Infoset	O
specification	O
provides	O
a	O
vocabulary	O
to	O
refer	O
to	O
the	O
constructs	O
within	O
an	O
XML	B-Protocol
document	I-Protocol
,	O
but	O
does	O
not	O
provide	O
any	O
guidance	O
on	O
how	O
to	O
access	O
this	O
information	O
.	O
</s>
<s>
A	O
variety	O
of	O
APIs	B-General_Concept
for	O
accessing	O
XML	B-Protocol
have	O
been	O
developed	O
and	O
used	O
,	O
and	O
some	O
have	O
been	O
standardized	O
.	O
</s>
<s>
Existing	O
APIs	B-General_Concept
for	O
XML	B-Protocol
processing	O
tend	O
to	O
fall	O
into	O
these	O
categories	O
:	O
</s>
<s>
Stream-oriented	O
APIs	B-General_Concept
accessible	O
from	O
a	O
programming	O
language	O
,	O
for	O
example	O
SAX	B-Application
and	O
StAX	B-Language
.	O
</s>
<s>
Tree-traversal	O
APIs	B-General_Concept
accessible	O
from	O
a	O
programming	O
language	O
,	O
for	O
example	O
DOM	B-General_Concept
.	O
</s>
<s>
XML	B-Language
data	I-Language
binding	I-Language
,	O
which	O
provides	O
an	O
automated	O
translation	O
between	O
an	O
XML	B-Protocol
document	I-Protocol
and	O
programming-language	O
objects	O
.	O
</s>
<s>
Declarative	O
transformation	O
languages	O
such	O
as	O
XSLT	B-Application
and	O
XQuery	B-Language
.	O
</s>
<s>
Syntax	O
extensions	O
to	O
general-purpose	O
programming	O
languages	O
,	O
for	O
example	O
LINQ	B-Language
and	O
Scala	B-Application
.	O
</s>
<s>
Stream-oriented	O
facilities	O
require	O
less	O
memory	O
and	O
,	O
for	O
certain	O
tasks	O
based	O
on	O
a	O
linear	O
traversal	O
of	O
an	O
XML	B-Protocol
document	I-Protocol
,	O
are	O
faster	O
and	O
simpler	O
than	O
other	O
alternatives	O
.	O
</s>
<s>
Tree-traversal	O
and	O
data-binding	O
APIs	B-General_Concept
typically	O
require	O
the	O
use	O
of	O
much	O
more	O
memory	O
,	O
but	O
are	O
often	O
found	O
more	O
convenient	O
for	O
use	O
by	O
programmers	O
;	O
some	O
include	O
declarative	O
retrieval	O
of	O
document	B-Protocol
components	O
via	O
the	O
use	O
of	O
XPath	B-Language
expressions	O
.	O
</s>
<s>
XSLT	B-Application
is	O
designed	O
for	O
declarative	O
description	O
of	O
XML	B-Protocol
document	I-Protocol
transformations	O
,	O
and	O
has	O
been	O
widely	O
implemented	O
both	O
in	O
server-side	O
packages	O
and	O
Web	O
browsers	O
.	O
</s>
<s>
XQuery	B-Language
overlaps	O
XSLT	B-Application
in	O
its	O
functionality	O
,	O
but	O
is	O
designed	O
more	O
for	O
searching	O
of	O
large	O
XML	B-Application
databases	I-Application
.	O
</s>
<s>
Simple	B-Application
API	I-Application
for	I-Application
XML	I-Application
(	O
SAX	B-Application
)	O
is	O
a	O
lexical	B-Application
,	O
event-driven	B-Application
API	B-General_Concept
in	O
which	O
a	O
document	B-Protocol
is	O
read	O
serially	O
and	O
its	O
contents	O
are	O
reported	O
as	O
callbacks	O
to	O
various	O
methods	B-Language
on	O
a	O
handler	O
object	O
of	O
the	O
user	O
's	O
design	O
.	O
</s>
<s>
SAX	B-Application
is	O
fast	O
and	O
efficient	O
to	O
implement	O
,	O
but	O
difficult	O
to	O
use	O
for	O
extracting	O
information	O
at	O
random	O
from	O
the	O
XML	B-Protocol
,	O
since	O
it	O
tends	O
to	O
burden	O
the	O
application	O
author	O
with	O
keeping	O
track	O
of	O
what	O
part	O
of	O
the	O
document	B-Protocol
is	O
being	O
processed	O
.	O
</s>
<s>
It	O
is	O
better	O
suited	O
to	O
situations	O
in	O
which	O
certain	O
types	O
of	O
information	O
are	O
always	O
handled	O
the	O
same	O
way	O
,	O
no	O
matter	O
where	O
they	O
occur	O
in	O
the	O
document	B-Protocol
.	O
</s>
<s>
Pull	O
parsing	O
treats	O
the	O
document	B-Protocol
as	O
a	O
series	O
of	O
items	O
read	O
in	O
sequence	O
using	O
the	O
iterator	B-Language
design	I-Language
pattern	I-Language
.	O
</s>
<s>
This	O
allows	O
for	O
writing	O
of	O
recursive	B-Application
descent	I-Application
parsers	I-Application
in	O
which	O
the	O
structure	O
of	O
the	O
code	O
performing	O
the	O
parsing	O
mirrors	O
the	O
structure	O
of	O
the	O
XML	B-Protocol
being	O
parsed	O
,	O
and	O
intermediate	O
parsed	O
results	O
can	O
be	O
used	O
and	O
accessed	O
as	O
local	O
variables	O
within	O
the	O
functions	O
performing	O
the	O
parsing	O
,	O
or	O
passed	O
down	O
(	O
as	O
function	O
parameters	O
)	O
into	O
lower-level	O
functions	O
,	O
or	O
returned	O
(	O
as	O
function	O
return	O
values	O
)	O
to	O
higher-level	O
functions	O
.	O
</s>
<s>
Examples	O
of	O
pull	O
parsers	O
include	O
Data::Edit::Xml	O
in	O
Perl	B-Language
,	O
StAX	B-Language
in	O
the	O
Java	B-Language
programming	I-Language
language	I-Language
,	O
XMLPullParser	O
in	O
Smalltalk	B-Application
,	O
XMLReader	O
in	O
PHP	B-Application
,	O
ElementTree.iterparse	O
in	O
Python	B-Language
,	O
System.Xml.XmlReader	O
in	O
the	O
.NET	B-Application
Framework	I-Application
,	O
and	O
the	B-General_Concept
DOM	I-General_Concept
traversal	O
API	B-General_Concept
(	O
NodeIterator	O
and	O
TreeWalker	O
)	O
.	O
</s>
<s>
A	O
pull	O
parser	O
creates	O
an	O
iterator	O
that	O
sequentially	O
visits	O
the	O
various	O
elements	O
,	O
attributes	O
,	O
and	O
data	O
in	O
an	O
XML	B-Protocol
document	I-Protocol
.	O
</s>
<s>
Code	O
that	O
uses	O
this	O
iterator	O
can	O
test	O
the	O
current	O
item	O
(	O
to	O
tell	O
,	O
for	O
example	O
,	O
whether	O
it	O
is	O
a	O
start-tag	O
or	O
end-tag	O
,	O
or	O
text	O
)	O
,	O
and	O
inspect	O
its	O
attributes	O
(	O
local	O
name	O
,	O
namespace	B-Language
,	O
values	O
of	O
XML	B-Protocol
attributes	O
,	O
value	O
of	O
text	O
,	O
etc	O
.	O
</s>
<s>
The	O
code	O
can	O
thus	O
extract	O
information	O
from	O
the	O
document	B-Protocol
as	O
it	O
traverses	O
it	O
.	O
</s>
<s>
The	O
recursive-descent	O
approach	O
tends	O
to	O
lend	O
itself	O
to	O
keeping	O
data	O
as	O
typed	O
local	O
variables	O
in	O
the	O
code	O
doing	O
the	O
parsing	O
,	O
while	O
SAX	B-Application
,	O
for	O
instance	O
,	O
typically	O
requires	O
a	O
parser	O
to	O
manually	O
maintain	O
intermediate	O
data	O
within	O
a	O
stack	O
of	O
elements	O
that	O
are	O
parent	O
elements	O
of	O
the	O
element	O
being	O
parsed	O
.	O
</s>
<s>
Pull-parsing	O
code	O
can	O
be	O
more	O
straightforward	O
to	O
understand	O
and	O
maintain	O
than	O
SAX	B-Application
parsing	O
code	O
.	O
</s>
<s>
Document	B-General_Concept
Object	I-General_Concept
Model	I-General_Concept
(	O
DOM	B-General_Concept
)	O
is	O
an	O
API	B-General_Concept
that	O
allows	O
for	O
navigation	O
of	O
the	O
entire	O
document	B-Protocol
as	O
if	O
it	O
were	O
a	O
tree	O
of	O
node	B-Data_Structure
objects	O
representing	O
the	O
document	B-Protocol
's	O
contents	O
.	O
</s>
<s>
A	O
DOM	B-General_Concept
document	B-Protocol
can	O
be	O
created	O
by	O
a	O
parser	O
,	O
or	O
can	O
be	O
generated	O
manually	O
by	O
users	O
(	O
with	O
limitations	O
)	O
.	O
</s>
<s>
Data	O
types	O
in	O
DOM	B-General_Concept
nodes	O
are	O
abstract	O
;	O
implementations	O
provide	O
their	O
own	O
programming	O
language-specific	O
bindings	B-Application
.	O
</s>
<s>
DOM	B-General_Concept
implementations	O
tend	O
to	O
be	O
memory	O
intensive	O
,	O
as	O
they	O
generally	O
require	O
the	O
entire	O
document	B-Protocol
to	O
be	O
loaded	O
into	O
memory	O
and	O
constructed	O
as	O
a	O
tree	O
of	O
objects	O
before	O
access	O
is	O
allowed	O
.	O
</s>
<s>
XML	B-Language
data	I-Language
binding	I-Language
is	O
a	O
powerful	O
technique	O
for	O
simplifying	O
the	O
development	O
of	O
applications	O
that	O
need	O
to	O
work	O
with	O
XML	B-Protocol
documents	I-Protocol
.	O
</s>
<s>
This	O
technique	O
involves	O
mapping	O
the	O
XML	B-Protocol
document	I-Protocol
to	O
a	O
hierarchy	O
of	O
strongly	O
typed	O
objects	O
,	O
rather	O
than	O
using	O
the	O
generic	O
objects	O
created	O
by	O
a	O
DOM	B-General_Concept
parser	O
.	O
</s>
<s>
XML	B-Language
data	I-Language
binding	I-Language
is	O
particularly	O
well-suited	O
for	O
applications	O
where	O
the	O
document	B-Protocol
structure	O
is	O
known	O
and	O
fixed	O
at	O
the	O
time	O
the	O
application	O
is	O
written	O
.	O
</s>
<s>
By	O
creating	O
a	O
strongly	O
typed	O
representation	O
of	O
the	O
XML	B-Protocol
data	O
,	O
developers	O
can	O
take	O
advantage	O
of	O
modern	O
integrated	O
development	O
environments	O
(	O
IDEs	O
)	O
that	O
provide	O
features	B-Architecture
like	O
auto-complete	O
,	O
code	O
refactoring	O
,	O
and	O
code	O
highlighting	O
.	O
</s>
<s>
Overall	O
,	O
XML	B-Language
data	I-Language
binding	I-Language
is	O
a	O
powerful	O
technique	O
for	O
building	O
robust	O
and	O
maintainable	O
applications	O
that	O
work	O
with	O
XML	B-Protocol
data	O
.	O
</s>
<s>
Example	O
data	O
binding	O
systems	O
include	O
the	O
Java	B-Language
Architecture	I-Language
for	I-Language
XML	I-Language
Binding	I-Language
(	O
JAXB	B-Language
)	O
,	O
XML	B-Protocol
Serialization	B-Application
in	O
.NET	B-Application
Framework	I-Application
.	O
</s>
<s>
and	O
XML	B-Protocol
serialization	B-Application
in	O
gSOAP	O
.	O
</s>
<s>
XML	B-Protocol
has	O
appeared	O
as	O
a	O
first-class	O
data	O
type	O
in	O
other	O
languages	O
.	O
</s>
<s>
The	O
ECMAScript	B-Language
for	I-Language
XML	I-Language
(	O
E4X	B-Language
)	O
extension	O
to	O
the	O
ECMAScript/JavaScript	O
language	O
explicitly	O
defines	O
two	O
specific	O
objects	O
(	O
XML	B-Protocol
and	O
XMLList	O
)	O
for	O
JavaScript	B-Language
,	O
which	O
support	O
XML	B-Protocol
document	I-Protocol
nodes	O
and	O
XML	B-Protocol
node	B-Data_Structure
lists	O
as	O
distinct	O
objects	O
and	O
use	O
a	O
dot-notation	O
specifying	O
parent-child	O
relationships	O
.	O
</s>
<s>
E4X	B-Language
is	O
supported	O
by	O
the	O
Mozilla	B-Operating_System
2.5	O
+	O
browsers	O
(	O
though	O
now	O
deprecated	O
)	O
and	O
Adobe	O
Actionscript	B-Operating_System
,	O
but	O
has	O
not	O
been	O
adopted	O
more	O
universally	O
.	O
</s>
<s>
Similar	O
notations	O
are	O
used	O
in	O
Microsoft	O
's	O
LINQ	B-Language
implementation	O
for	O
Microsoft	O
.NET	B-Application
3.5	O
and	O
above	O
,	O
and	O
in	O
Scala	B-Application
(	O
which	O
uses	O
the	O
Java	B-Language
VM	O
)	O
.	O
</s>
<s>
The	O
open-source	O
xmlsh	O
application	O
,	O
which	O
provides	O
a	O
Linux-like	O
shell	O
with	O
special	O
features	B-Architecture
for	O
XML	B-Protocol
manipulation	O
,	O
similarly	O
treats	O
XML	B-Protocol
as	O
a	O
data	O
type	O
,	O
using	O
the	O
<[ ]>	O
notation	O
.	O
</s>
<s>
The	O
Resource	O
Description	O
Framework	O
defines	O
a	O
data	O
type	O
rdf:XMLLiteral	O
to	O
hold	O
wrapped	O
,	O
canonical	O
XML	B-Protocol
.	O
</s>
<s>
Facebook	O
has	O
produced	O
extensions	O
to	O
the	O
PHP	B-Application
and	O
JavaScript	B-Language
languages	I-Language
that	O
add	O
XML	B-Protocol
to	O
the	O
core	O
syntax	O
in	O
a	O
similar	O
fashion	O
to	O
E4X	B-Language
,	O
namely	O
XHP	B-Language
and	O
JSX	O
respectively	O
.	O
</s>
<s>
XML	B-Protocol
is	O
an	O
application	O
profile	O
of	O
SGML	B-Language
(	O
ISO	B-Language
8879	I-Language
)	O
.	O
</s>
<s>
The	O
versatility	O
of	O
SGML	B-Language
for	O
dynamic	O
information	O
display	O
was	O
understood	O
by	O
early	O
digital	O
media	O
publishers	O
in	O
the	O
late	O
1980s	O
prior	O
to	O
the	O
rise	O
of	O
the	O
Internet	O
.	O
</s>
<s>
By	O
the	O
mid-1990s	O
some	O
practitioners	O
of	O
SGML	B-Language
had	O
gained	O
experience	O
with	O
the	O
then-new	O
World	O
Wide	O
Web	O
,	O
and	O
believed	O
that	O
SGML	B-Language
offered	O
solutions	O
to	O
some	O
of	O
the	O
problems	O
the	O
Web	O
was	O
likely	O
to	O
face	O
as	O
it	O
grew	O
.	O
</s>
<s>
Dan	O
Connolly	O
added	O
SGML	B-Language
to	O
the	O
list	O
of	O
W3C	O
's	O
activities	O
when	O
he	O
joined	O
the	O
staff	O
in	O
1995	O
;	O
work	O
began	O
in	O
mid-1996	O
when	O
Sun	O
Microsystems	O
engineer	O
Jon	O
Bosak	O
developed	O
a	O
charter	O
and	O
recruited	O
collaborators	O
.	O
</s>
<s>
Bosak	O
was	O
well	O
connected	O
in	O
the	O
small	O
community	O
of	O
people	O
who	O
had	O
experience	O
both	O
in	O
SGML	B-Language
and	O
the	O
Web	O
.	O
</s>
<s>
XML	B-Protocol
was	O
compiled	O
by	O
a	O
working	O
group	O
of	O
eleven	O
members	O
,	O
supported	O
by	O
a	O
(	O
roughly	O
)	O
150-member	O
Interest	O
Group	O
.	O
</s>
<s>
James	O
Clark	O
served	O
as	O
Technical	O
Lead	O
of	O
the	O
Working	O
Group	O
,	O
notably	O
contributing	O
the	O
empty-element	O
<empty />	O
syntax	O
and	O
the	O
name	O
"	O
XML	B-Protocol
"	O
.	O
</s>
<s>
The	O
XML	B-Protocol
Working	O
Group	O
was	O
a	O
distributed	O
team	O
that	O
relied	O
on	O
a	O
variety	O
of	O
communication	O
channels	O
to	O
collaborate	O
on	O
the	O
development	O
of	O
the	O
standard	O
.	O
</s>
<s>
Despite	O
these	O
challenges	O
,	O
the	O
group	O
was	O
able	O
to	O
work	O
effectively	O
and	O
make	O
important	O
progress	O
towards	O
defining	O
the	O
syntax	O
and	O
semantics	B-Application
of	O
XML	B-Protocol
.	O
</s>
<s>
The	O
major	O
design	O
decisions	O
were	O
reached	O
in	O
a	O
short	O
burst	O
of	O
intense	O
work	O
between	O
August	O
and	O
November	O
1996	O
,	O
when	O
the	O
first	O
Working	O
Draft	O
of	O
an	O
XML	B-Protocol
specification	I-Protocol
was	O
published	O
.	O
</s>
<s>
Further	O
design	O
work	O
continued	O
through	O
1997	O
,	O
and	O
XML	B-Protocol
1.0	O
became	O
a	O
W3C	O
Recommendation	O
on	O
February	O
10	O
,	O
1998	O
.	O
</s>
