<s>
Extensible	B-Language
HyperText	I-Language
Markup	I-Language
Language	I-Language
(	O
XHTML	B-Language
)	O
is	O
part	O
of	O
the	O
family	O
of	O
XML	B-Protocol
markup	O
languages	O
.	O
</s>
<s>
It	O
mirrors	O
or	O
extends	O
versions	O
of	O
the	O
widely	O
used	O
HyperText	B-Language
Markup	I-Language
Language	I-Language
(	O
HTML	B-Language
)	O
,	O
the	O
language	O
in	O
which	O
Web	O
pages	O
are	O
formulated	O
.	O
</s>
<s>
While	O
HTML	B-Language
,	O
prior	O
to	O
HTML5	B-Application
,	O
was	O
defined	O
as	O
an	O
application	O
of	O
Standard	B-Language
Generalized	I-Language
Markup	I-Language
Language	I-Language
(	O
SGML	B-Language
)	O
,	O
a	O
flexible	O
markup	O
language	O
framework	O
,	O
XHTML	B-Language
is	O
an	O
application	O
of	O
XML	B-Protocol
,	O
a	O
more	O
restrictive	O
subset	O
of	O
SGML	B-Language
.	O
</s>
<s>
XHTML	B-Language
documents	O
are	O
well-formed	B-Language
and	O
may	O
therefore	O
be	O
parsed	O
using	O
standard	O
XML	B-Protocol
parsers	I-Protocol
,	O
unlike	O
HTML	B-Language
,	O
which	O
requires	O
a	O
lenient	O
HTML-specific	O
parser	O
.	O
</s>
<s>
XHTML	B-Language
1.0	I-Language
became	O
a	O
World	O
Wide	O
Web	O
Consortium	O
(	O
W3C	O
)	O
recommendation	O
on	O
26	O
January	O
2000	O
.	O
</s>
<s>
XHTML	B-Language
1.1	O
became	O
a	O
W3C	O
recommendation	O
on	O
31	O
May	O
2001	O
.	O
</s>
<s>
XHTML	B-Language
is	O
now	O
referred	O
to	O
as	O
"	O
the	O
XML	B-Protocol
syntax	O
for	O
HTML	B-Language
"	O
and	O
being	O
developed	O
as	O
an	O
XML	B-Protocol
adaptation	O
of	O
the	O
HTML	B-Language
living	O
standard	O
.	O
</s>
<s>
XHTML	B-Language
1.0	I-Language
was	O
"	O
a	O
reformulation	O
of	O
the	O
three	O
HTML	B-Language
4	O
document	O
types	O
as	O
applications	O
of	O
XML	B-Protocol
1.0	O
"	O
.	O
</s>
<s>
The	O
World	O
Wide	O
Web	O
Consortium	O
(	O
W3C	O
)	O
also	O
simultaneously	O
maintained	O
the	O
HTML	B-Language
4.01	I-Language
Recommendation	O
.	O
</s>
<s>
In	O
the	O
XHTML	B-Language
1.0	I-Language
Recommendation	I-Language
document	O
,	O
as	O
published	O
and	O
revised	O
in	O
August	O
2002	O
,	O
the	O
W3C	O
commented	O
that	O
"	O
The	O
XHTML	B-Language
family	O
is	O
the	O
next	O
step	O
in	O
the	O
evolution	O
of	O
the	O
Internet	O
.	O
</s>
<s>
By	O
migrating	O
to	O
XHTML	B-Language
today	O
,	O
content	O
developers	O
can	O
enter	O
the	O
XML	B-Protocol
world	O
with	O
all	O
of	O
its	O
attendant	O
benefits	O
,	O
while	O
still	O
remaining	O
confident	O
in	O
their	O
content	O
's	O
backward	O
and	O
future	O
compatibility.	O
"	O
</s>
<s>
However	O
,	O
in	O
2005	O
,	O
the	O
Web	B-Language
Hypertext	I-Language
Application	I-Language
Technology	I-Language
Working	I-Language
Group	I-Language
(	O
WHATWG	B-Language
)	O
formed	O
,	O
independently	O
of	O
the	O
W3C	O
,	O
to	O
work	O
on	O
advancing	O
ordinary	O
HTML	B-Language
not	O
based	O
on	O
XHTML	B-Language
.	O
</s>
<s>
The	O
WHATWG	B-Language
eventually	O
began	O
working	O
on	O
a	O
standard	O
that	O
supported	O
both	O
XML	B-Protocol
and	O
non-XML	O
serializations	B-Application
,	O
HTML5	B-Application
,	O
in	O
parallel	O
to	O
W3C	O
standards	O
such	O
as	O
XHTML	B-Language
2.0	O
.	O
</s>
<s>
In	O
2007	O
,	O
the	O
W3C	O
's	O
HTML	B-Language
working	O
group	O
voted	O
to	O
officially	O
recognize	O
HTML5	B-Application
and	O
work	O
on	O
it	O
as	O
the	O
next-generation	O
HTML	B-Language
standard	O
.	O
</s>
<s>
In	O
2009	O
,	O
the	O
W3C	O
allowed	O
the	O
XHTML	B-Language
2.0	O
Working	O
Group	O
's	O
charter	O
to	O
expire	O
,	O
acknowledging	O
that	O
HTML5	B-Application
would	O
be	O
the	O
sole	O
next-generation	O
HTML	B-Language
standard	O
,	O
including	O
both	O
XML	B-Protocol
and	O
non-XML	O
serializations	B-Application
.	O
</s>
<s>
Of	O
the	O
two	O
serializations	B-Application
,	O
the	O
W3C	O
suggests	O
that	O
most	O
authors	O
use	O
the	O
HTML	B-Language
syntax	I-Language
,	O
rather	O
than	O
the	O
XHTML	B-Language
syntax	O
.	O
</s>
<s>
The	O
W3C	O
recommendations	O
of	O
both	O
XHTML	B-Language
1.0	I-Language
and	O
XHTML	B-Language
1.1	O
were	O
retired	O
on	O
27	O
March	O
2018	O
,	O
along	O
with	O
HTML	B-Language
4.0	I-Language
,	O
HTML	B-Language
4.01	I-Language
,	O
and	O
HTML5	B-Application
.	O
</s>
<s>
XHTML	B-Language
was	O
developed	O
to	O
make	O
HTML	B-Language
more	O
extensible	B-Architecture
and	O
increase	O
interoperability	O
with	O
other	O
data	O
formats	O
.	O
</s>
<s>
In	O
addition	O
,	O
browsers	O
were	O
forgiving	O
of	O
errors	O
in	O
HTML	B-Language
,	O
and	O
most	O
websites	O
were	O
displayed	O
despite	O
technical	O
errors	O
in	O
the	O
markup	O
;	O
XHTML	B-Language
introduced	O
stricter	O
error	O
handling	O
.	O
</s>
<s>
HTML	B-Language
4	O
was	O
ostensibly	O
an	O
application	O
of	O
Standard	B-Language
Generalized	I-Language
Markup	I-Language
Language	I-Language
(	O
SGML	B-Language
)	O
;	O
however	O
the	O
specification	O
for	O
SGML	B-Language
was	O
complex	O
,	O
and	O
neither	O
web	O
browsers	O
nor	O
the	O
HTML	B-Language
4	O
Recommendation	O
were	O
fully	O
conformant	O
to	O
it	O
.	O
</s>
<s>
The	O
XML	B-Protocol
standard	O
,	O
approved	O
in	O
1998	O
,	O
provided	O
a	O
simpler	O
data	O
format	O
closer	O
in	O
simplicity	O
to	O
HTML	B-Language
4	O
.	O
</s>
<s>
By	O
shifting	O
to	O
an	O
XML	B-Protocol
format	O
,	O
it	O
was	O
hoped	O
HTML	B-Language
would	O
become	O
compatible	O
with	O
common	O
XML	B-Protocol
tools	O
;	O
servers	O
and	O
proxies	O
would	O
be	O
able	O
to	O
transform	O
content	O
,	O
as	O
necessary	O
,	O
for	O
constrained	O
devices	O
such	O
as	O
mobile	O
phones	O
.	O
</s>
<s>
By	O
using	O
namespaces	B-Language
,	O
XHTML	B-Language
documents	O
could	O
provide	O
extensibility	B-Architecture
by	O
including	O
fragments	O
from	O
other	O
XML-based	O
languages	O
such	O
as	O
Scalable	B-Application
Vector	I-Application
Graphics	I-Application
and	O
MathML	B-Language
.	O
</s>
<s>
Finally	O
,	O
the	O
renewed	O
work	O
would	O
provide	O
an	O
opportunity	O
to	O
divide	O
HTML	B-Language
into	O
reusable	O
components	O
(	O
XHTML	B-Language
Modularization	O
)	O
and	O
clean	O
up	O
untidy	O
parts	O
of	O
the	O
language	O
.	O
</s>
<s>
There	O
are	O
various	O
differences	O
between	O
XHTML	B-Language
and	O
HTML	B-Language
.	O
</s>
<s>
The	O
Document	B-General_Concept
Object	I-General_Concept
Model	I-General_Concept
(	O
DOM	B-General_Concept
)	O
is	O
a	O
tree	O
structure	O
that	O
represents	O
the	O
page	O
internally	O
in	O
applications	O
,	O
and	O
XHTML	B-Language
and	O
HTML	B-Language
are	O
two	O
different	O
ways	O
of	O
representing	O
that	O
in	O
markup	O
.	O
</s>
<s>
Both	O
are	O
less	O
expressive	O
than	O
the	B-General_Concept
DOM	I-General_Concept
–	O
for	O
example	O
,	O
"	O
--	O
 "	O
may	O
be	O
placed	O
in	O
comments	O
in	O
the	B-General_Concept
DOM	I-General_Concept
,	O
but	O
cannot	O
be	O
represented	O
in	O
a	O
comment	O
in	O
either	O
XHTML	B-Language
or	O
HTML	B-Language
–	O
and	O
generally	O
,	O
XHTML	B-Language
's	O
XML	B-Protocol
syntax	O
is	O
more	O
expressive	O
than	O
HTML	B-Language
(	O
for	O
example	O
,	O
arbitrary	O
namespaces	B-Language
are	O
not	O
allowed	O
in	O
HTML	B-Language
)	O
.	O
</s>
<s>
XHTML	B-Language
uses	O
an	O
XML	B-Protocol
syntax	O
,	O
while	O
HTML	B-Language
uses	O
a	O
pseudo-SGML	O
syntax	O
(	O
officially	O
SGML	B-Language
for	O
HTML4	O
and	O
under	O
,	O
but	O
never	O
in	O
practice	O
,	O
and	O
standardized	O
away	O
from	O
SGML	B-Language
in	O
HTML5	B-Application
)	O
.	O
</s>
<s>
Because	O
the	O
expressible	O
contents	O
of	O
the	B-General_Concept
DOM	I-General_Concept
in	O
syntax	O
are	O
slightly	O
different	O
,	O
there	O
are	O
some	O
changes	O
in	O
actual	O
behavior	O
between	O
the	O
two	O
models	O
.	O
</s>
<s>
Broadly	O
,	O
the	O
XML	B-Protocol
rules	O
require	O
that	O
all	O
elements	B-General_Concept
be	O
closed	O
,	O
either	O
by	O
a	O
separate	O
closing	O
tag	B-General_Concept
or	O
using	O
the	O
self-closing	O
syntax	O
(	O
e.g.	O
</s>
<s>
XML	B-Protocol
is	O
case-sensitive	O
for	O
element	O
and	O
attribute	B-General_Concept
names	O
,	O
while	O
HTML	B-Language
is	O
not	O
.	O
</s>
<s>
Some	O
shorthand	O
features	O
in	O
HTML	B-Language
are	O
omitted	O
in	O
XML	B-Protocol
,	O
such	O
as	O
(	O
1	O
)	O
attribute	B-General_Concept
minimization	O
,	O
where	O
attribute	B-General_Concept
values	O
or	O
their	O
quotes	O
may	O
be	O
omitted	O
(	O
e.g.	O
</s>
<s>
or	O
,	O
while	O
in	O
XML	B-Protocol
this	O
must	O
be	O
expressed	O
as	O
)	O
;	O
(	O
2	O
)	O
element	O
minimization	O
may	O
be	O
used	O
to	O
remove	O
elements	B-General_Concept
entirely	O
(	O
such	O
as	O
inferred	O
in	O
a	O
table	O
if	O
not	O
given	O
)	O
;	O
and	O
(	O
3	O
)	O
the	O
rarely	O
used	O
SGML	B-Language
syntax	O
for	O
element	O
minimization	O
(	O
"	O
shorttag	O
"	O
)	O
,	O
which	O
most	O
browsers	O
do	O
not	O
implement	O
.	O
</s>
<s>
There	O
are	O
numerous	O
other	O
technical	O
requirements	O
surrounding	O
namespaces	B-Language
and	O
precise	O
parsing	O
of	O
whitespace	O
and	O
certain	O
characters	O
and	O
elements	B-General_Concept
.	O
</s>
<s>
The	O
exact	O
parsing	O
of	O
HTML	B-Language
in	O
practice	O
has	O
been	O
undefined	O
until	O
recently	O
;	O
see	O
the	O
HTML5	B-Application
specification	O
(	O
)	O
for	O
full	O
details	O
,	O
or	O
the	O
working	O
summary	O
(	O
)	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
syntactical	O
differences	O
,	O
there	O
are	O
some	O
behavioral	O
differences	O
,	O
mostly	O
arising	O
from	O
the	O
underlying	O
differences	O
in	O
serialization	B-Application
.	O
</s>
<s>
A	O
fatal	O
parse	O
error	O
in	O
XML	B-Protocol
(	O
such	O
as	O
an	O
incorrect	O
tag	B-General_Concept
structure	O
)	O
causes	O
document	O
processing	O
to	O
be	O
aborted	O
.	O
</s>
<s>
Most	O
content	O
requiring	O
namespaces	B-Language
will	O
not	O
work	O
in	O
HTML	B-Language
,	O
except	O
the	O
built-in	O
support	O
for	O
SVG	B-Application
and	O
MathML	B-Language
in	O
the	O
HTML5	B-Application
parser	O
along	O
with	O
certain	O
magic	O
prefixes	O
such	O
as	O
xlink	O
.	O
</s>
<s>
JavaScript	O
processing	O
is	O
different	O
in	O
XHTML	B-Language
,	O
with	O
minor	O
changes	O
in	O
case	O
sensitivity	O
to	O
some	O
functions	O
,	O
and	O
further	O
precautions	O
to	O
restrict	O
processing	O
to	O
well-formed	B-Language
content	O
.	O
</s>
<s>
Scripts	O
must	O
not	O
use	O
the	O
method	O
;	O
it	O
is	O
not	O
available	O
for	O
XHTML	B-Language
.	O
</s>
<s>
The	O
innerHTML	O
property	O
is	O
available	O
,	O
but	O
will	O
not	O
insert	O
non-well-formed	O
content	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
it	O
can	O
be	O
used	O
to	O
insert	O
well-formed	B-Language
namespaced	O
content	O
into	O
XHTML	B-Language
.	O
</s>
<s>
Cascading	B-Language
Style	I-Language
Sheets	I-Language
(	O
CSS	B-Language
)	O
are	O
also	O
applied	O
differently	O
.	O
</s>
<s>
Due	O
to	O
XHTML	B-Language
's	O
case-sensitivity	O
,	O
all	O
CSS	B-Language
selectors	O
become	O
case-sensitive	O
for	O
XHTML	B-Language
documents	O
.	O
</s>
<s>
Some	O
CSS	B-Language
properties	O
,	O
such	O
as	O
backgrounds	O
,	O
set	O
on	O
the	O
element	O
in	O
HTML	B-Language
are	O
'	O
inherited	O
upwards	O
 '	O
into	O
the	O
element	O
;	O
this	O
appears	O
not	O
to	O
be	O
the	O
case	O
for	O
XHTML	B-Language
.	O
</s>
<s>
The	O
similarities	O
between	O
HTML	B-Language
4.01	I-Language
and	O
XHTML	B-Language
1.0	I-Language
led	O
many	O
websites	O
and	O
content	B-Protocol
management	I-Protocol
systems	I-Protocol
to	O
adopt	O
the	O
initial	O
W3C	O
XHTML	B-Language
1.0	I-Language
Recommendation	I-Language
.	O
</s>
<s>
To	O
aid	O
authors	O
in	O
the	O
transition	O
,	O
the	O
W3C	O
provided	O
guidance	O
on	O
how	O
to	O
publish	O
XHTML	B-Language
1.0	I-Language
documents	O
in	O
an	O
HTML-compatible	O
manner	O
,	O
and	O
serve	O
them	O
to	O
browsers	O
that	O
were	O
not	O
designed	O
for	O
XHTML	B-Language
.	O
</s>
<s>
Such	O
"	O
HTML-compatible	O
"	O
content	O
is	O
sent	O
using	O
the	O
HTML	B-Language
media	B-Application
type	I-Application
(	O
text/html	B-Language
)	O
rather	O
than	O
the	O
official	O
Internet	B-Application
media	I-Application
type	I-Application
for	O
XHTML	B-Language
(	O
application/xhtml	O
+xml	O
)	O
.	O
</s>
<s>
When	O
measuring	O
the	O
adoption	O
of	O
XHTML	B-Language
to	O
that	O
of	O
regular	O
HTML	B-Language
,	O
therefore	O
,	O
it	O
is	O
important	O
to	O
distinguish	O
whether	O
it	O
is	O
media	B-Application
type	I-Application
usage	O
or	O
actual	O
document	O
contents	O
that	O
are	O
being	O
compared	O
.	O
</s>
<s>
Most	O
web	O
browsers	O
have	O
mature	O
support	O
for	O
all	O
of	O
the	O
possible	O
XHTML	B-Language
media	B-Application
types	I-Application
.	O
</s>
<s>
The	O
notable	O
exception	O
is	O
Internet	B-Application
Explorer	I-Application
versions	O
8	O
and	O
earlier	O
by	O
Microsoft	O
;	O
rather	O
than	O
rendering	O
application/xhtml	O
+xml	O
content	O
,	O
a	O
dialog	O
box	O
invites	O
the	O
user	O
to	O
save	O
the	O
content	O
to	O
disk	O
instead	O
.	O
</s>
<s>
Both	O
Internet	B-Application
Explorer	I-Application
7	O
(	O
released	O
in	O
2006	O
)	O
and	O
Internet	B-Application
Explorer	I-Application
8	O
(	O
released	O
in	O
March	O
2009	O
)	O
exhibit	O
this	O
behavior	O
.	O
</s>
<s>
Microsoft	O
developer	O
Chris	O
Wilson	O
explained	O
in	O
2005	O
that	O
IE7	O
's	O
priorities	O
were	O
improved	O
browser	B-Protocol
security	I-Protocol
and	O
CSS	B-Language
support	O
,	O
and	O
that	O
proper	O
XHTML	B-Language
support	O
would	O
be	O
difficult	O
to	O
graft	O
onto	O
IE	O
's	O
compatibility-oriented	O
HTML	B-Language
parser	O
;	O
however	O
,	O
Microsoft	O
added	O
support	O
for	O
true	O
XHTML	B-Language
in	O
IE9	B-Application
.	O
</s>
<s>
As	O
long	O
as	O
support	O
is	O
not	O
widespread	O
,	O
most	O
web	O
developers	O
avoid	O
using	O
XHTML	B-Language
that	O
is	O
not	O
HTML-compatible	O
,	O
so	O
advantages	O
of	O
XML	B-Protocol
such	O
as	O
namespaces	B-Language
,	O
faster	O
parsing	O
,	O
and	O
smaller-footprint	O
browsers	O
do	O
not	O
benefit	O
the	O
user	O
.	O
</s>
<s>
In	O
the	O
early	O
2000s	O
,	O
some	O
Web	O
developers	O
began	O
to	O
question	O
why	O
Web	O
authors	O
ever	O
made	O
the	O
leap	O
into	O
authoring	O
in	O
XHTML	B-Language
.	O
</s>
<s>
Others	O
countered	O
that	O
the	O
problems	O
ascribed	O
to	O
the	O
use	O
of	O
XHTML	B-Language
could	O
mostly	O
be	O
attributed	O
to	O
two	O
main	O
sources	O
:	O
the	O
production	O
of	O
invalid	O
XHTML	B-Language
documents	O
by	O
some	O
Web	O
authors	O
and	O
the	O
lack	O
of	O
support	O
for	O
XHTML	B-Language
built	O
into	O
Internet	B-Application
Explorer	I-Application
6	I-Application
.	O
</s>
<s>
They	O
went	O
on	O
to	O
describe	O
the	O
benefits	O
of	O
XML-based	O
Web	O
documents	O
(	O
i.e.	O
</s>
<s>
XHTML	B-Language
)	O
regarding	O
searching	O
,	O
indexing	O
,	O
and	O
parsing	O
as	O
well	O
as	O
future-proofing	O
the	O
Web	O
itself	O
.	O
</s>
<s>
In	O
October	O
2006	O
,	O
HTML	B-Language
inventor	O
and	O
W3C	O
chair	O
Tim	O
Berners-Lee	O
,	O
introducing	O
a	O
major	O
W3C	O
effort	O
to	O
develop	O
a	O
new	O
HTML	B-Language
specification	O
,	O
posted	O
in	O
his	O
blog	O
that	O
,	O
"	O
The	O
attempt	O
to	O
get	O
the	O
world	O
to	O
switch	O
to	O
XML	B-Protocol
...	O
all	O
at	O
once	O
did	O
n't	O
work	O
.	O
</s>
<s>
The	O
large	O
HTML-generating	O
public	O
did	O
not	O
move	O
...	O
</s>
<s>
Some	O
large	O
communities	O
did	O
shift	O
and	O
are	O
enjoying	O
the	O
fruits	O
of	O
well-formed	B-Language
systems	O
...	O
</s>
<s>
The	O
plan	O
is	O
to	O
charter	O
a	O
completely	O
new	O
HTML	B-Language
group.	O
"	O
</s>
<s>
The	O
current	O
HTML5	B-Application
working	O
draft	O
says	O
"	O
special	O
attention	O
has	O
been	O
given	O
to	O
defining	O
clear	O
conformance	O
criteria	O
for	O
user	O
agents	O
in	O
an	O
effort	O
to	O
improve	O
interoperability	O
...	O
while	O
at	O
the	O
same	O
time	O
updating	O
the	O
HTML	B-Language
specifications	O
to	O
address	O
issues	O
raised	O
in	O
the	O
past	O
few	O
years.	O
"	O
</s>
<s>
Ian	O
Hickson	O
,	O
editor	O
of	O
the	O
HTML5	B-Application
specification	O
criticizing	O
the	O
improper	O
use	O
of	O
XHTML	B-Language
in	O
2002	O
,	O
is	O
a	O
member	O
of	O
the	O
group	O
developing	O
this	O
specification	O
and	O
is	O
listed	O
as	O
one	O
of	O
the	O
co-editors	O
of	O
the	O
current	O
working	O
draft	O
.	O
</s>
<s>
Simon	O
Pieters	O
researched	O
the	O
XML-compliance	O
of	O
mobile	O
browsers	O
and	O
concluded	O
"	O
the	O
claim	O
that	O
XHTML	B-Language
would	O
be	O
needed	O
for	O
mobile	O
devices	O
is	O
simply	O
a	O
myth	O
"	O
.	O
</s>
<s>
December	O
1998	O
saw	O
the	O
publication	O
of	O
a	O
W3C	O
Working	O
Draft	O
entitled	O
Reformulating	O
HTML	B-Language
in	O
XML	B-Protocol
.	O
</s>
<s>
This	O
introduced	O
Voyager	O
,	O
the	O
codename	O
for	O
a	O
new	O
markup	O
language	O
based	O
on	O
HTML	B-Language
4	O
,	O
but	O
adhering	O
to	O
the	O
stricter	O
syntax	O
rules	O
of	O
XML	B-Protocol
.	O
</s>
<s>
By	O
February	O
1999	O
the	O
name	O
of	O
the	O
specification	O
had	O
changed	O
to	O
XHTML	B-Language
1.0	I-Language
:	O
The	O
Extensible	B-Language
HyperText	I-Language
Markup	I-Language
Language	I-Language
,	O
and	O
in	O
January	O
2000	O
it	O
was	O
officially	O
adopted	O
as	O
a	O
W3C	O
Recommendation	O
.	O
</s>
<s>
There	O
are	O
three	O
formal	O
DTDs	B-Language
for	O
XHTML	B-Language
1.0	I-Language
,	O
corresponding	O
to	O
the	O
three	O
different	O
versions	O
of	O
HTML	B-Language
4.01	I-Language
:	O
</s>
<s>
XHTML	B-Language
1.0	I-Language
Strict	O
is	O
the	O
XML	B-Protocol
equivalent	O
to	O
strict	O
HTML	B-Language
4.01	I-Language
,	O
and	O
includes	O
elements	B-General_Concept
and	O
attributes	O
that	O
have	O
not	O
been	O
marked	O
deprecated	O
in	O
the	O
HTML	B-Language
4.01	I-Language
specification	O
.	O
</s>
<s>
,	O
XHTML	B-Language
1.0	I-Language
Strict	O
is	O
the	O
document	O
type	O
used	O
for	O
the	O
homepage	O
of	O
the	O
website	O
of	O
the	O
World	O
Wide	O
Web	O
Consortium	O
.	O
</s>
<s>
XHTML	B-Language
1.0	I-Language
Transitional	O
is	O
the	O
XML	B-Protocol
equivalent	O
of	O
HTML	B-Language
4.01	I-Language
Transitional	O
,	O
and	O
includes	O
the	O
presentational	O
elements	B-General_Concept
(	O
such	O
as	O
center	O
,	O
font	O
and	O
strike	O
)	O
excluded	O
from	O
the	O
strict	O
version	O
.	O
</s>
<s>
XHTML	B-Language
1.0	I-Language
Frameset	B-General_Concept
is	O
the	O
XML	B-Protocol
equivalent	O
of	O
HTML	B-Language
4.01	I-Language
Frameset	B-General_Concept
,	O
and	O
allows	O
for	O
the	O
definition	O
of	O
frameset	B-General_Concept
documents	I-General_Concept
—	O
a	O
common	O
Web	O
feature	O
in	O
the	O
late	O
1990s	O
.	O
</s>
<s>
The	O
second	O
edition	O
of	O
XHTML	B-Language
1.0	I-Language
became	O
a	O
W3C	O
Recommendation	O
in	O
August	O
2002	O
.	O
</s>
<s>
Modularization	O
provides	O
an	O
abstract	O
collection	O
of	O
components	O
through	O
which	O
XHTML	B-Language
can	O
be	O
subsetted	O
and	O
extended	O
.	O
</s>
<s>
The	O
feature	O
is	O
intended	O
to	O
help	O
XHTML	B-Language
extend	O
its	O
reach	O
onto	O
emerging	O
platforms	O
,	O
such	O
as	O
mobile	O
devices	O
and	O
Web-enabled	O
televisions	O
.	O
</s>
<s>
The	O
initial	O
draft	O
of	O
Modularization	O
of	O
XHTML	B-Language
became	O
available	O
in	O
April	O
1999	O
,	O
and	O
reached	O
Recommendation	O
status	O
in	O
April	O
2001	O
.	O
</s>
<s>
The	O
first	O
modular	O
XHTML	B-Language
variants	O
were	O
XHTML	B-Language
1.1	O
and	O
XHTML	B-Language
Basic	O
1.0	O
.	O
</s>
<s>
In	O
October	O
2008	O
Modularization	O
of	O
XHTML	B-Language
was	O
superseded	O
by	O
XHTML	B-Language
Modularization	O
1.1	O
,	O
which	O
adds	O
an	O
XML	B-Protocol
Schema	O
implementation	O
.	O
</s>
<s>
XHTML	B-Language
1.1	O
evolved	O
out	O
of	O
the	O
work	O
surrounding	O
the	O
initial	O
Modularization	O
of	O
XHTML	B-Language
specification	O
.	O
</s>
<s>
The	O
modules	O
combined	O
within	O
XHTML	B-Language
1.1	O
effectively	O
recreate	O
XHTML	B-Language
1.0	I-Language
Strict	O
,	O
with	O
the	O
addition	O
of	O
ruby	O
annotation	O
elements	B-General_Concept
(	O
ruby	O
,	O
rbc	O
,	O
rtc	O
,	O
rb	O
,	O
rt	O
and	O
rp	O
)	O
to	O
better	O
support	O
East-Asian	O
languages	O
.	O
</s>
<s>
Other	O
changes	O
include	O
the	O
removal	O
of	O
the	O
name	O
attribute	B-General_Concept
from	O
the	O
a	O
and	O
map	O
elements	B-General_Concept
,	O
and	O
(	O
in	O
the	O
first	O
edition	O
of	O
the	O
language	O
)	O
the	O
removal	O
of	O
the	O
lang	O
attribute	B-General_Concept
in	O
favor	O
of	O
xml	B-Protocol
:	O
lang	O
.	O
</s>
<s>
Although	O
XHTML	B-Language
1.1	O
is	O
largely	O
compatible	O
with	O
XHTML	B-Language
1.0	I-Language
and	O
HTML	B-Language
4	O
,	O
in	O
August	O
2002	O
the	O
Working	O
Group	O
issued	O
a	O
formal	O
Note	O
advising	O
that	O
it	O
should	O
not	O
be	O
transmitted	O
with	O
the	O
HTML	B-Language
media	B-Application
type	I-Application
.	O
</s>
<s>
With	O
limited	O
browser	O
support	O
for	O
the	O
alternate	O
application/xhtml	O
+xml	O
media	B-Application
type	I-Application
,	O
XHTML	B-Language
1.1	O
proved	O
unable	O
to	O
gain	O
widespread	O
use	O
.	O
</s>
<s>
In	O
January	O
2009	O
a	O
second	O
edition	O
of	O
the	O
document	O
(	O
XHTML	B-Language
Media	B-Application
Types	I-Application
–	O
Second	O
Edition	O
)	O
was	O
issued	O
,	O
relaxing	O
this	O
restriction	O
and	O
allowing	O
XHTML	B-Language
1.1	O
to	O
be	O
served	O
as	O
text/html	B-Language
.	O
</s>
<s>
The	O
second	O
edition	O
of	O
XHTML	B-Language
1.1	O
was	O
issued	O
on	O
23	O
November	O
2010	O
,	O
which	O
addresses	O
various	O
errata	O
and	O
adds	O
an	O
XML	B-Protocol
Schema	O
implementation	O
not	O
included	O
in	O
the	O
original	O
specification	O
.	O
</s>
<s>
Since	O
information	B-Device
appliances	I-Device
may	O
lack	O
the	O
system	B-General_Concept
resources	I-General_Concept
to	O
implement	O
all	O
XHTML	B-Language
abstract	O
modules	O
,	O
the	O
W3C	O
defined	O
a	O
feature-limited	O
XHTML	B-Language
specification	O
called	O
XHTML	B-Language
Basic	O
.	O
</s>
<s>
Of	O
all	O
the	O
versions	O
of	O
XHTML	B-Language
,	O
XHTML	B-Language
Basic	O
1.0	O
provides	O
the	O
fewest	O
features	O
.	O
</s>
<s>
With	O
XHTML	B-Language
1.1	O
,	O
it	O
is	O
one	O
of	O
the	O
two	O
first	O
implementations	O
of	O
modular	O
XHTML	B-Language
.	O
</s>
<s>
XHTML	B-Language
Basic	O
1.1	O
replaces	O
the	O
Basic	O
Forms	O
Module	O
with	O
the	O
Forms	O
Module	O
and	O
adds	O
the	O
Intrinsic	O
Events	O
,	O
Presentation	O
,	O
and	O
Scripting	O
modules	O
.	O
</s>
<s>
It	O
also	O
supports	O
additional	O
tags	B-General_Concept
and	O
attributes	O
from	O
other	O
modules	O
.	O
</s>
<s>
The	O
current	O
version	O
of	O
XHTML	B-Language
Basic	O
is	O
1.1	O
Second	O
Edition	O
(	O
23	O
November	O
2010	O
)	O
,	O
in	O
which	O
the	O
language	O
is	O
re-implemented	O
in	O
the	O
W3C	O
's	O
XML	B-Protocol
Schema	O
language	O
.	O
</s>
<s>
This	O
version	O
also	O
supports	O
the	O
lang	O
attribute	B-General_Concept
.	O
</s>
<s>
XHTML-Print	O
,	O
which	O
became	O
a	O
W3C	O
Recommendation	O
in	O
September	O
2006	O
,	O
is	O
a	O
specialized	O
version	O
of	O
XHTML	B-Language
Basic	O
designed	O
for	O
documents	O
printed	O
from	O
information	B-Device
appliances	I-Device
to	O
low-end	O
printers	O
.	O
</s>
<s>
XHTML	B-Language
Mobile	O
Profile	O
(	O
abbreviated	O
XHTML	B-Language
MP	O
or	O
XHTML-MP	O
)	O
is	O
a	O
third-party	O
variant	O
of	O
the	O
W3C	O
's	O
XHTML	B-Language
Basic	O
specification	O
.	O
</s>
<s>
Like	O
XHTML	B-Language
Basic	O
,	O
XHTML	B-Language
was	O
developed	O
for	O
information	B-Device
appliances	I-Device
with	O
limited	O
system	B-General_Concept
resources	I-General_Concept
.	O
</s>
<s>
In	O
October	O
2001	O
,	O
a	O
limited	O
company	O
called	O
the	O
Wireless	B-Protocol
Application	I-Protocol
Protocol	I-Protocol
Forum	O
began	O
adapting	O
XHTML	B-Language
Basic	O
for	O
WAP	O
2.0	O
,	O
the	O
second	O
major	O
version	O
of	O
the	O
Wireless	B-Protocol
Application	I-Protocol
Protocol	I-Protocol
.	O
</s>
<s>
WAP	O
Forum	O
based	O
their	O
DTD	O
on	O
the	O
W3C	O
's	O
Modularization	O
of	O
XHTML	B-Language
,	O
incorporating	O
the	O
same	O
modules	O
the	O
W3C	O
used	O
in	O
XHTML	B-Language
Basic	O
1.0	O
—	O
except	O
for	O
the	O
Target	O
Module	O
.	O
</s>
<s>
Starting	O
with	O
this	O
foundation	O
,	O
the	O
WAP	O
Forum	O
replaced	O
the	O
Basic	O
Forms	O
Module	O
with	O
a	O
partial	O
implementation	O
of	O
the	O
Forms	O
Module	O
,	O
added	O
partial	O
support	O
for	O
the	O
Legacy	O
and	O
Presentation	O
modules	O
,	O
and	O
added	O
full	O
support	O
for	O
the	O
Style	O
Attribute	B-General_Concept
Module	O
.	O
</s>
<s>
In	O
2002	O
,	O
the	O
WAP	O
Forum	O
has	O
subsumed	O
into	O
the	O
Open	O
Mobile	O
Alliance	O
(	O
OMA	O
)	O
,	O
which	O
continued	O
to	O
develop	O
XHTML	B-Language
Mobile	O
Profile	O
as	O
a	O
component	O
of	O
their	O
OMA	O
Browsing	O
Specification	O
.	O
</s>
<s>
XHTML	B-Language
MP	O
1.1	O
is	O
part	O
of	O
v2.1	O
of	O
the	O
OMA	O
Browsing	O
Specification	O
(	O
1	O
November	O
2002	O
)	O
.	O
</s>
<s>
This	O
version	O
,	O
finalized	O
on	O
27	O
February	O
2007	O
,	O
expands	O
the	O
capabilities	O
of	O
XHTML	B-Language
MP	O
1.1	O
with	O
full	O
support	O
for	O
the	O
Forms	O
Module	O
and	O
OMA	O
Text	O
Input	O
Modes	O
.	O
</s>
<s>
XHTML	B-Language
MP	O
1.2	O
is	O
part	O
of	O
v2.3	O
of	O
the	O
OMA	O
Browsing	O
Specification	O
(	O
13	O
March	O
2007	O
)	O
.	O
</s>
<s>
XHTML	B-Language
MP	O
1.3	O
(	O
finalized	O
on	O
23	O
September	O
2008	O
)	O
uses	O
the	O
XHTML	B-Language
Basic	O
1.1	O
document	B-Language
type	I-Language
definition	I-Language
,	O
which	O
includes	O
the	O
Target	O
Module	O
.	O
</s>
<s>
Events	O
in	O
this	O
version	O
of	O
the	O
specification	O
are	O
updated	O
to	O
DOM	B-General_Concept
Level	O
3	O
specifications	O
(	O
i.e.	O
,	O
they	O
are	O
platform	O
-	O
and	O
language-neutral	O
)	O
.	O
</s>
<s>
The	O
XHTML	B-Language
2	O
Working	O
Group	O
considered	O
the	O
creation	O
of	O
a	O
new	O
language	O
based	O
on	O
XHTML	B-Language
1.1	O
.	O
</s>
<s>
If	O
XHTML	B-Language
1.2	O
was	O
created	O
,	O
it	O
would	O
include	O
WAI-ARIA	B-General_Concept
and	O
role	O
attributes	O
to	O
better	O
support	O
accessible	O
web	O
applications	O
,	O
and	O
improved	O
Semantic	B-General_Concept
Web	O
support	O
through	O
RDFa	B-General_Concept
.	O
</s>
<s>
The	O
inputmode	O
attribute	B-General_Concept
from	O
XHTML	B-Language
Basic	O
1.1	O
,	O
along	O
with	O
the	O
target	O
attribute	B-General_Concept
(	O
for	O
specifying	O
frame	B-General_Concept
targets	O
)	O
might	O
also	O
be	O
present	O
.	O
</s>
<s>
Since	O
the	O
W3C	O
announced	O
that	O
it	O
does	O
not	O
intend	O
to	O
recharter	O
the	O
XHTML2	O
WG	O
,	O
and	O
closed	O
the	O
WG	O
in	O
December	O
2010	O
,	O
this	O
means	O
that	O
XHTML	B-Language
1.2	O
proposal	O
would	O
not	O
eventuate	O
.	O
</s>
<s>
Between	O
August	O
2002	O
and	O
July	O
2006	O
,	O
the	O
W3C	O
released	O
eight	O
Working	O
Drafts	O
of	O
XHTML	B-Language
2.0	O
,	O
a	O
new	O
version	O
of	O
XHTML	B-Language
able	O
to	O
make	O
a	O
clean	O
break	O
from	O
the	O
past	O
by	O
discarding	O
the	O
requirement	O
of	O
backward	O
compatibility	O
.	O
</s>
<s>
This	O
lack	O
of	O
compatibility	O
with	O
XHTML	B-Language
1.x	O
and	O
HTML	B-Language
4	O
caused	O
some	O
early	O
controversy	O
in	O
the	O
web	O
developer	O
community	O
.	O
</s>
<s>
Some	O
parts	O
of	O
the	O
language	O
(	O
such	O
as	O
the	O
role	O
and	O
RDFa	B-General_Concept
attributes	O
)	O
were	O
subsequently	O
split	O
out	O
of	O
the	O
specification	O
and	O
worked	O
on	O
as	O
separate	O
modules	O
,	O
partially	O
to	O
help	O
make	O
the	O
transition	O
from	O
XHTML	B-Language
1.x	O
to	O
XHTML	B-Language
2.0	O
smoother	O
.	O
</s>
<s>
The	O
ninth	O
draft	O
of	O
XHTML	B-Language
2.0	O
was	O
expected	O
to	O
appear	O
in	O
2009	O
,	O
but	O
on	O
2	O
July	O
2009	O
,	O
the	O
W3C	O
decided	O
to	O
let	O
the	O
XHTML2	O
Working	O
Group	O
charter	O
expire	O
by	O
that	O
year	O
's	O
end	O
,	O
effectively	O
halting	O
any	O
further	O
development	O
of	O
the	O
draft	O
into	O
a	O
standard	O
.	O
</s>
<s>
Instead	O
,	O
XHTML	B-Language
2.0	O
and	O
its	O
related	O
documents	O
were	O
released	O
as	O
W3C	O
Notes	O
in	O
2010	O
.	O
</s>
<s>
New	O
features	O
to	O
have	O
been	O
introduced	O
by	O
XHTML	B-Language
2.0	O
included	O
:	O
</s>
<s>
HTML	B-Language
forms	O
were	O
to	O
be	O
replaced	O
by	O
XForms	B-Application
,	O
an	O
XML-based	O
user	O
input	O
specification	O
allowing	O
forms	O
to	O
be	O
displayed	O
appropriately	O
for	O
different	O
rendering	O
devices	O
.	O
</s>
<s>
HTML	B-General_Concept
frames	I-General_Concept
were	O
to	O
be	O
replaced	O
by	O
XFrames	O
.	O
</s>
<s>
The	B-General_Concept
DOM	I-General_Concept
Events	O
were	O
to	O
be	O
replaced	O
by	O
XML	B-Language
Events	I-Language
,	O
which	O
uses	O
the	O
XML	B-Protocol
Document	I-Protocol
Object	O
Model	O
.	O
</s>
<s>
However	O
,	O
XLink	O
itself	O
is	O
not	O
compatible	O
with	O
XHTML	B-Language
due	O
to	O
design	O
differences	O
.	O
</s>
<s>
Any	O
element	O
was	O
to	O
be	O
able	O
to	O
reference	O
alternative	O
media	O
with	O
the	O
src	O
attribute	B-General_Concept
,	O
e.g.	O
,	O
is	O
the	O
same	O
as	O
.	O
</s>
<s>
The	O
alt	O
attribute	B-General_Concept
of	O
the	O
img	O
element	O
was	O
removed	O
:	O
alternative	O
text	O
was	O
to	O
be	O
given	O
in	O
the	O
content	O
of	O
the	O
img	O
element	O
,	O
much	O
like	O
the	O
object	O
element	O
,	O
e.g.	O
,	O
.	O
</s>
<s>
The	O
remaining	O
presentational	O
elements	B-General_Concept
i	O
,	O
b	O
and	O
tt	O
,	O
still	O
allowed	O
in	O
XHTML	B-Language
1.x	O
(	O
even	O
Strict	O
)	O
,	O
were	O
to	O
be	O
absent	O
from	O
XHTML	B-Language
2.0	O
.	O
</s>
<s>
The	O
only	O
somewhat	O
presentational	O
elements	B-General_Concept
remaining	O
were	O
to	O
be	O
sup	O
and	O
sub	O
for	O
superscript	O
and	O
subscript	O
respectively	O
because	O
they	O
have	O
significant	O
non-presentational	O
uses	O
and	O
are	O
required	O
by	O
certain	O
languages	O
.	O
</s>
<s>
All	O
other	O
tags	B-General_Concept
were	O
meant	O
to	O
be	O
semantic	B-General_Concept
instead	O
(	O
e.g.	O
</s>
<s>
strong	O
for	O
strong	O
emphasis	O
)	O
while	O
allowing	O
the	O
user	O
agent	O
to	O
control	O
the	O
presentation	O
of	O
elements	B-General_Concept
via	O
CSS	B-Language
(	O
e.g.	O
</s>
<s>
The	O
addition	O
of	O
RDF	O
triple	O
with	O
the	O
property	O
and	O
about	O
attributes	O
to	O
facilitate	O
the	O
conversion	O
from	O
XHTML	B-Language
to	O
RDF/XML	O
.	O
</s>
<s>
HTML5	B-Application
grew	O
independently	O
of	O
the	O
W3C	O
,	O
through	O
a	O
loose	O
group	O
of	O
browser	O
manufacturers	O
and	O
other	O
interested	O
parties	O
calling	O
themselves	O
the	O
WHATWG	B-Language
,	O
or	O
Web	B-Language
Hypertext	I-Language
Application	I-Language
Technology	I-Language
Working	I-Language
Group	I-Language
.	O
</s>
<s>
The	O
key	O
motive	O
of	O
the	O
group	O
was	O
to	O
create	O
a	O
platform	O
for	O
dynamic	O
web	O
applications	O
;	O
they	O
considered	O
XHTML	B-Language
2.0	O
to	O
be	O
too	O
document-centric	O
,	O
and	O
not	O
suitable	O
for	O
the	O
creation	O
of	O
internet	B-Application
forum	I-Application
sites	O
or	O
online	O
shops	O
.	O
</s>
<s>
HTML5	B-Application
has	O
both	O
a	O
regular	O
text/html	B-Language
serialization	B-Application
and	O
an	O
XML	B-Protocol
serialization	B-Application
,	O
which	O
is	O
also	O
known	O
as	O
XHTML5	O
.	O
</s>
<s>
The	O
language	O
is	O
more	O
compatible	O
with	O
HTML	B-Language
4	O
and	O
XHTML	B-Language
1.x	O
than	O
XHTML	B-Language
2.0	O
,	O
due	O
to	O
the	O
decision	O
to	O
keep	O
the	O
existing	O
HTML	B-Language
form	O
elements	B-General_Concept
and	O
events	O
model	O
.	O
</s>
<s>
It	O
adds	O
many	O
new	O
elements	B-General_Concept
not	O
found	O
in	O
XHTML	B-Language
1	O
.	O
x	O
,	O
however	O
,	O
such	O
as	O
section	O
and	O
aside	O
tags	B-General_Concept
.	O
</s>
<s>
The	O
XHTML5	O
language	O
,	O
like	O
HTML5	B-Application
,	O
uses	O
a	O
DOCTYPE	O
declaration	O
without	O
a	O
DTD	O
.	O
</s>
<s>
Furthermore	O
,	O
the	O
specification	O
deprecates	O
earlier	O
XHTML	B-Language
DTDs	B-Language
by	O
asking	O
the	O
browsers	O
to	O
replace	O
them	O
with	O
one	O
containing	O
only	O
entity	O
definitions	O
for	O
named	O
characters	O
during	O
parsing	O
.	O
</s>
<s>
XHTML+RDFa	O
is	O
an	O
extended	O
version	O
of	O
the	O
XHTML	B-Language
markup	O
language	O
for	O
supporting	O
RDF	O
through	O
a	O
collection	O
of	O
attributes	O
and	O
processing	O
rules	O
in	O
the	O
form	O
of	O
well-formed	B-Language
XML	I-Language
documents	I-Language
.	O
</s>
<s>
This	O
host	O
language	O
is	O
one	O
of	O
the	O
techniques	O
used	O
to	O
develop	O
Semantic	B-General_Concept
Web	O
content	O
by	O
embedding	O
rich	O
semantic	B-General_Concept
markup	I-General_Concept
.	O
</s>
<s>
An	O
XHTML	B-Language
document	O
that	O
conforms	O
to	O
an	O
XHTML	B-Language
specification	O
is	O
said	O
to	O
be	O
valid	O
.	O
</s>
<s>
The	O
root	B-Language
element	I-Language
of	O
an	O
XHTML	B-Language
document	O
must	O
be	O
html	B-Language
,	O
and	O
must	O
contain	O
an	O
xmlns	B-Language
attribute	B-General_Concept
to	O
associate	O
it	O
with	O
the	O
XHTML	B-Language
namespace	B-Language
.	O
</s>
<s>
The	O
namespace	B-Language
URI	O
for	O
XHTML	B-Language
is	O
http://www.w3.org/1999/xhtml	O
.	O
</s>
<s>
The	O
example	O
tag	B-General_Concept
below	O
additionally	O
features	O
an	O
xml:lang	B-Protocol
attribute	B-General_Concept
to	O
identify	O
the	O
document	O
with	O
a	O
natural	O
language	O
:	O
</s>
<s>
In	O
order	O
to	O
validate	O
an	O
XHTML	B-Language
document	O
,	O
a	O
Document	O
Type	O
Declaration	O
,	O
or	O
DOCTYPE	O
,	O
may	O
be	O
used	O
.	O
</s>
<s>
A	O
DOCTYPE	O
declares	O
to	O
the	O
browser	O
the	O
Document	B-Language
Type	I-Language
Definition	I-Language
(	O
DTD	O
)	O
to	O
which	O
the	O
document	O
conforms	O
.	O
</s>
<s>
A	O
Document	O
Type	O
Declaration	O
should	O
be	O
placed	O
before	O
the	O
root	B-Language
element	I-Language
.	O
</s>
<s>
The	O
system	B-Language
identifier	I-Language
part	O
of	O
the	O
DOCTYPE	O
,	O
which	O
in	O
these	O
examples	O
is	O
the	O
URL	O
that	O
begins	O
with	O
http://,	O
need	O
only	O
point	O
to	O
a	O
copy	O
of	O
the	O
DTD	O
to	O
use	O
,	O
if	O
the	O
validator	O
cannot	O
locate	O
one	O
based	O
on	O
the	O
public	O
identifier	O
(	O
the	O
other	O
quoted	O
string	O
)	O
.	O
</s>
<s>
A	O
character	B-General_Concept
encoding	I-General_Concept
may	O
be	O
specified	O
at	O
the	O
beginning	O
of	O
an	O
XHTML	B-Language
document	O
in	O
the	O
XML	B-Protocol
declaration	O
when	O
the	O
document	O
is	O
served	O
using	O
the	O
application/xhtml	O
+xml	O
MIME	B-Application
type	I-Application
.	O
</s>
<s>
(	O
If	O
an	O
XML	B-Protocol
document	I-Protocol
lacks	O
encoding	O
specification	O
,	O
an	O
XML	B-Protocol
parser	I-Protocol
assumes	O
that	O
the	O
encoding	O
is	O
UTF-8	O
or	O
UTF-16	O
,	O
unless	O
the	O
encoding	O
has	O
already	O
been	O
determined	O
by	O
a	O
higher	O
protocol	O
.	O
)	O
</s>
<s>
However	O
,	O
if	O
the	O
document	O
instead	O
makes	O
use	O
of	O
XML	B-Protocol
1.1	O
or	O
another	O
character	B-General_Concept
encoding	I-General_Concept
,	O
a	O
declaration	O
is	O
necessary	O
.	O
</s>
<s>
Internet	B-Application
Explorer	I-Application
prior	O
to	O
version	O
7	O
enters	O
quirks	B-General_Concept
mode	I-General_Concept
,	O
if	O
it	O
encounters	O
an	O
XML	B-Protocol
declaration	O
in	O
a	O
document	O
served	O
as	O
text/html	B-Language
.	O
</s>
<s>
XHTML	B-Language
1.x	O
documents	O
are	O
mostly	O
backward	O
compatible	O
with	O
HTML	B-Language
4	O
user	O
agents	O
when	O
the	O
appropriate	O
guidelines	O
are	O
followed	O
.	O
</s>
<s>
XHTML	B-Language
1.1	O
is	O
essentially	O
compatible	O
,	O
although	O
the	O
elements	B-General_Concept
for	O
ruby	O
annotation	O
are	O
not	O
part	O
of	O
the	O
HTML	B-Language
4	O
specification	O
and	O
thus	O
generally	O
ignored	O
by	O
HTML	B-Language
4	O
browsers	O
.	O
</s>
<s>
Later	O
XHTML	B-Language
1.x	O
modules	O
such	O
as	O
those	O
for	O
the	O
role	O
attribute	B-General_Concept
,	O
RDFa	B-General_Concept
,	O
and	O
WAI-ARIA	B-General_Concept
degrade	O
gracefully	O
in	O
a	O
similar	O
manner	O
.	O
</s>
<s>
XHTML	B-Language
2.0	O
is	O
significantly	O
less	O
compatible	O
,	O
although	O
this	O
can	O
be	O
mitigated	O
to	O
some	O
degree	O
through	O
the	O
use	O
of	O
scripting	O
.	O
</s>
<s>
(	O
This	O
can	O
be	O
simple	O
one-liners	O
,	O
such	O
as	O
the	O
use	O
of	O
document.createElement( )	O
to	O
register	O
a	O
new	O
HTML	B-General_Concept
element	I-General_Concept
within	O
Internet	B-Application
Explorer	I-Application
,	O
or	O
complete	O
JavaScript	O
frameworks	O
,	O
such	O
as	O
the	O
FormFaces	O
implementation	O
of	O
XForms	B-Application
.	O
)	O
</s>
<s>
The	O
following	O
are	O
examples	O
of	O
XHTML	B-Language
1.0	I-Language
Strict	O
,	O
with	O
both	O
having	O
the	O
same	O
visual	O
output	O
.	O
</s>
<s>
The	O
former	O
one	O
follows	O
the	O
HTML	B-Language
Compatibility	O
Guidelines	O
of	O
the	O
XHTML	B-Language
Media	B-Application
Types	I-Application
Note	O
while	O
the	O
latter	O
one	O
breaks	O
backward	O
compatibility	O
,	O
but	O
provides	O
cleaner	O
markup	O
.	O
</s>
<s>
The	O
"	O
loadpdf	O
"	O
function	O
is	O
actually	O
a	O
workaround	O
for	O
Internet	B-Application
Explorer	I-Application
.	O
</s>
<s>
The	O
img	O
element	O
does	O
not	O
get	O
a	O
name	O
attribute	B-General_Concept
in	O
the	O
.	O
</s>
<s>
HTML5	B-Application
and	O
XHTML5	O
serializations	B-Application
are	O
largely	O
inter-compatible	O
if	O
adhering	O
to	O
the	O
stricter	O
XHTML5	O
syntax	O
,	O
but	O
there	O
are	O
some	O
cases	O
in	O
which	O
XHTML	B-Language
will	O
not	O
work	O
as	O
valid	O
HTML5	B-Application
(	O
e.g.	O
,	O
processing	B-Language
instructions	I-Language
are	O
deprecated	O
in	O
,	O
are	O
treated	O
as	O
comments	O
,	O
and	O
close	O
on	O
the	O
first	O
"	O
>	O
"	O
,	O
whereas	O
they	O
are	O
fully	O
allowed	O
in	O
XML	B-Protocol
,	O
are	O
treated	O
as	O
their	O
own	O
type	O
,	O
and	O
close	O
on	O
?	O
>	O
)	O
.	O
</s>
