<s>
The	O
HyperText	B-Language
Markup	I-Language
Language	I-Language
or	O
HTML	B-Language
is	O
the	O
standard	O
markup	O
language	O
for	O
documents	O
designed	O
to	O
be	O
displayed	O
in	O
a	O
web	B-Application
browser	I-Application
.	O
</s>
<s>
It	O
is	O
often	O
assisted	O
by	O
technologies	O
such	O
as	O
Cascading	B-Language
Style	I-Language
Sheets	I-Language
(	O
CSS	B-Language
)	O
and	O
scripting	B-Language
languages	I-Language
such	O
as	O
JavaScript	B-Language
.	O
</s>
<s>
Web	B-Application
browsers	I-Application
receive	O
HTML	B-Language
documents	O
from	O
a	O
web	B-Application
server	I-Application
or	O
from	O
local	O
storage	O
and	O
render	B-Protocol
the	O
documents	O
into	O
multimedia	O
web	O
pages	O
.	O
</s>
<s>
HTML	B-Language
describes	O
the	O
structure	O
of	O
a	O
web	O
page	O
semantically	O
and	O
originally	O
included	O
cues	O
for	O
its	O
appearance	O
.	O
</s>
<s>
HTML	B-General_Concept
elements	I-General_Concept
are	O
the	O
building	O
blocks	O
of	O
HTML	B-Language
pages	O
.	O
</s>
<s>
With	O
HTML	B-Language
constructs	O
,	O
images	O
and	O
other	O
objects	O
such	O
as	O
interactive	O
forms	O
may	O
be	O
embedded	O
into	O
the	O
rendered	O
page	O
.	O
</s>
<s>
HTML	B-Language
provides	O
a	O
means	O
to	O
create	O
structured	O
documents	O
by	O
denoting	O
structural	O
semantics	B-Application
for	O
text	O
such	O
as	O
headings	O
,	O
paragraphs	O
,	O
lists	O
,	O
links	O
,	O
quotes	O
,	O
and	O
other	O
items	O
.	O
</s>
<s>
HTML	B-General_Concept
elements	I-General_Concept
are	O
delineated	O
by	O
tags	B-General_Concept
,	O
written	O
using	O
angle	O
brackets	O
.	O
</s>
<s>
Tags	B-General_Concept
such	O
as	O
and	O
directly	O
introduce	O
content	O
into	O
the	O
page	O
.	O
</s>
<s>
Other	O
tags	B-General_Concept
such	O
as	O
and	O
surround	O
and	O
provide	O
information	O
about	O
document	O
text	O
and	O
may	O
include	O
sub-element	O
tags	B-General_Concept
.	O
</s>
<s>
Browsers	B-Application
do	O
not	O
display	O
the	O
HTML	B-General_Concept
tags	I-General_Concept
but	O
use	O
them	O
to	O
interpret	O
the	O
content	O
of	O
the	O
page	O
.	O
</s>
<s>
HTML	B-Language
can	O
embed	O
programs	O
written	O
in	O
a	O
scripting	B-Language
language	I-Language
such	O
as	O
JavaScript	B-Language
,	O
which	O
affects	O
the	O
behavior	O
and	O
content	O
of	O
web	O
pages	O
.	O
</s>
<s>
The	O
inclusion	O
of	O
CSS	B-Language
defines	O
the	O
look	O
and	O
layout	O
of	O
content	O
.	O
</s>
<s>
The	O
World	O
Wide	O
Web	O
Consortium	O
(	O
W3C	O
)	O
,	O
former	O
maintainer	O
of	O
the	O
HTML	B-Language
and	O
current	O
maintainer	O
of	O
the	O
CSS	B-Language
standards	O
,	O
has	O
encouraged	O
the	O
use	O
of	O
CSS	B-Language
over	O
explicit	O
presentational	O
HTML	B-Language
A	O
form	O
of	O
HTML	B-Language
,	O
known	O
as	O
HTML5	B-Application
,	O
is	O
used	O
to	O
display	O
video	O
and	O
audio	O
,	O
primarily	O
using	O
the	O
element	O
,	O
together	O
with	O
JavaScript	B-Language
.	O
</s>
<s>
In	O
1980	O
,	O
physicist	O
Tim	O
Berners-Lee	O
,	O
a	O
contractor	O
at	O
CERN	O
,	O
proposed	O
and	O
prototyped	O
ENQUIRE	B-Protocol
,	O
a	O
system	O
for	O
CERN	O
researchers	O
to	O
use	O
and	O
share	O
documents	O
.	O
</s>
<s>
Berners-Lee	O
specified	O
HTML	B-Language
and	O
wrote	O
the	O
browser	B-Application
and	O
server	O
software	O
in	O
late	O
1990	O
.	O
</s>
<s>
That	O
year	O
,	O
Berners-Lee	O
and	O
CERN	O
data	B-Application
systems	I-Application
engineer	O
Robert	O
Cailliau	O
collaborated	O
on	O
a	O
joint	O
request	O
for	O
funding	O
,	O
but	O
the	O
project	O
was	O
not	O
formally	O
adopted	O
by	O
CERN	O
.	O
</s>
<s>
The	O
first	O
publicly	O
available	O
description	O
of	O
HTML	B-Language
was	O
a	O
document	O
called	O
"	O
HTML	B-General_Concept
Tags	I-General_Concept
"	O
,	O
first	O
mentioned	O
on	O
the	O
Internet	O
by	O
Tim	O
Berners-Lee	O
in	O
late	O
1991	O
.	O
</s>
<s>
It	O
describes	O
18	O
elements	O
comprising	O
the	O
initial	O
,	O
relatively	O
simple	O
design	O
of	O
HTML	B-Language
.	O
</s>
<s>
Except	O
for	O
the	O
hyperlink	O
tag	B-General_Concept
,	O
these	O
were	O
strongly	O
influenced	O
by	O
SGMLguid	B-General_Concept
,	O
an	O
in-house	O
Standard	B-Language
Generalized	I-Language
Markup	I-Language
Language	I-Language
(	O
SGML	B-Language
)	O
-based	O
documentation	O
format	O
at	O
CERN	O
.	O
</s>
<s>
Eleven	O
of	O
these	O
elements	O
still	O
exist	O
in	O
HTML	B-Language
4	O
.	O
</s>
<s>
HTML	B-Language
is	O
a	O
markup	O
language	O
that	O
web	B-Application
browsers	I-Application
use	O
to	O
interpret	O
and	O
compose	O
text	O
,	O
images	O
,	O
and	O
other	O
material	O
into	O
visible	O
or	O
audible	O
web	O
pages	O
.	O
</s>
<s>
Default	O
characteristics	O
for	O
every	O
item	O
of	O
HTML	B-General_Concept
markup	I-General_Concept
are	O
defined	O
in	O
the	O
browser	B-Application
,	O
and	O
these	O
characteristics	O
can	O
be	O
altered	O
or	O
enhanced	O
by	O
the	O
web	O
page	O
designer	O
's	O
additional	O
use	O
of	O
CSS	B-Language
.	O
</s>
<s>
Many	O
of	O
the	O
text	O
elements	O
are	O
mentioned	O
in	O
the	O
1988	O
ISO	O
technical	O
report	O
TR	O
9537	O
Techniques	O
for	O
using	O
SGML	B-Language
,	O
which	O
describes	O
the	O
features	O
of	O
early	O
text	O
formatting	O
languages	O
such	O
as	O
that	O
used	O
by	O
the	O
RUNOFF	B-Protocol
command	I-Protocol
developed	O
in	O
the	O
early	O
1960s	O
for	O
the	O
CTSS	B-Operating_System
(	O
Compatible	B-Operating_System
Time-Sharing	I-Operating_System
System	I-Operating_System
)	O
operating	O
system	O
.	O
</s>
<s>
However	O
,	O
the	O
SGML	B-Language
concept	O
of	O
generalized	O
markup	O
is	O
based	O
on	O
elements	O
(	O
nested	O
annotated	O
ranges	O
with	O
attributes	O
)	O
rather	O
than	O
merely	O
print	O
effects	O
,	O
with	O
separate	O
structure	O
and	O
markup	O
.	O
</s>
<s>
HTML	B-Language
has	O
been	O
progressively	O
moved	O
in	O
this	O
direction	O
with	O
CSS	B-Language
.	O
</s>
<s>
Berners-Lee	O
considered	O
HTML	B-Language
to	O
be	O
an	O
application	O
of	O
SGML	B-Language
.	O
</s>
<s>
It	O
was	O
formally	O
defined	O
as	O
such	O
by	O
the	O
Internet	O
Engineering	O
Task	O
Force	O
(	O
IETF	O
)	O
with	O
the	O
mid-1993	O
publication	O
of	O
the	O
first	O
proposal	O
for	O
an	O
HTML	B-Language
specification	O
,	O
the	O
"	O
Hypertext	B-Language
Markup	I-Language
Language	I-Language
(	O
HTML	B-Language
)	O
"	O
Internet	O
Draft	O
by	O
Berners-Lee	O
and	O
Dan	O
Connolly	O
,	O
which	O
included	O
an	O
SGML	B-Language
Document	B-Language
type	I-Language
definition	I-Language
to	O
define	O
the	O
syntax	O
.	O
</s>
<s>
The	O
draft	O
expired	O
after	O
six	O
months	O
,	O
but	O
was	O
notable	O
for	O
its	O
acknowledgment	O
of	O
the	O
NCSA	B-Application
Mosaic	I-Application
browser	B-Application
's	O
custom	O
tag	B-General_Concept
for	O
embedding	O
in-line	O
images	O
,	O
reflecting	O
the	O
IETF	O
's	O
philosophy	O
of	O
basing	O
standards	O
on	O
successful	O
prototypes	O
.	O
</s>
<s>
Similarly	O
,	O
Dave	O
Raggett	O
's	O
competing	O
Internet	O
Draft	O
,	O
"	O
HTML+	B-Language
(	O
Hypertext	O
Markup	O
Format	O
)	O
"	O
,	O
from	O
late	O
1993	O
,	O
suggested	O
standardizing	O
already-implemented	O
features	O
like	O
tables	O
and	O
fill-out	O
forms	O
.	O
</s>
<s>
After	O
the	O
HTML	B-Language
and	O
HTML+	B-Language
drafts	O
expired	O
in	O
early	O
1994	O
,	O
the	O
IETF	O
created	O
an	O
HTML	B-Language
Working	O
Group	O
.	O
</s>
<s>
In	O
1995	O
,	O
this	O
working	O
group	O
completed	O
"	O
HTML	B-Language
2.0	O
"	O
,	O
the	O
first	O
HTML	B-Language
specification	O
intended	O
to	O
be	O
treated	O
as	O
a	O
standard	O
against	O
which	O
future	O
implementations	O
should	O
be	O
based	O
.	O
</s>
<s>
the	O
HTML	B-Language
specifications	O
have	O
been	O
maintained	O
,	O
with	O
input	O
from	O
commercial	O
software	O
vendors	O
,	O
by	O
the	O
World	O
Wide	O
Web	O
Consortium	O
(	O
W3C	O
)	O
.	O
</s>
<s>
In	O
2000	O
,	O
HTML	B-Language
became	O
an	O
international	O
standard	O
(	O
ISO/IEC	O
15445:2000	O
)	O
.	O
</s>
<s>
HTML	B-Language
4.01	I-Language
was	O
published	O
in	O
late	O
1999	O
,	O
with	O
further	O
errata	O
published	O
through	O
2001	O
.	O
</s>
<s>
In	O
2004	O
,	O
development	O
began	O
on	O
HTML5	B-Application
in	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
,	O
which	O
became	O
a	O
joint	O
deliverable	O
with	O
the	O
W3C	O
in	O
2008	O
,	O
and	O
was	O
completed	O
and	O
standardized	O
on	O
28	O
October	O
2014	O
.	O
</s>
<s>
November	O
24	O
,	O
1995	O
HTML	B-Language
2.0	O
was	O
published	O
as	O
.	O
</s>
<s>
January	O
14	O
,	O
1997	O
HTML	B-Language
3.2	O
was	O
published	O
as	O
a	O
W3C	O
Recommendation	O
.	O
</s>
<s>
It	O
was	O
the	O
first	O
version	O
developed	O
and	O
standardized	O
exclusively	O
by	O
the	O
W3C	O
,	O
as	O
the	O
IETF	O
had	O
closed	O
its	O
HTML	B-Language
Working	O
Group	O
on	O
September	O
12	O
,	O
1996	O
.	O
</s>
<s>
Initially	O
code-named	O
"	O
Wilbur	O
"	O
,	O
HTML	B-Language
3.2	O
dropped	O
math	O
formulas	O
entirely	O
,	O
reconciled	O
overlap	O
among	O
various	O
proprietary	O
extensions	O
and	O
adopted	O
most	O
of	O
Netscape	B-Protocol
's	O
visual	O
markup	O
tags	B-General_Concept
.	O
</s>
<s>
Netscape	B-Protocol
's	O
blink	B-Application
element	I-Application
and	O
Microsoft	O
's	O
marquee	B-General_Concept
element	I-General_Concept
were	O
omitted	O
due	O
to	O
a	O
mutual	O
agreement	O
between	O
the	O
two	O
companies	O
.	O
</s>
<s>
A	O
markup	O
for	O
mathematical	O
formulas	O
similar	O
to	O
that	O
of	O
HTML	B-Language
was	O
standardized	O
14	O
months	O
later	O
in	O
MathML	B-Language
.	O
</s>
<s>
December	O
18	O
,	O
1997	O
HTML	B-Language
4.0	I-Language
was	O
published	O
as	O
a	O
W3C	O
Recommendation	O
.	O
</s>
<s>
Frameset	B-General_Concept
,	O
in	O
which	O
mostly	O
only	O
frame	B-General_Concept
related	O
elements	O
are	O
allowed	O
.	O
</s>
<s>
Initially	O
code-named	O
"	O
Cougar	O
"	O
,	O
HTML	B-Language
4.0	I-Language
adopted	O
many	O
browser-specific	O
element	O
types	O
and	O
attributes	O
,	O
but	O
also	O
sought	O
to	O
phase	O
out	O
Netscape	B-Protocol
's	O
visual	O
markup	O
features	O
by	O
marking	O
them	O
as	O
deprecated	B-General_Concept
in	O
favor	O
of	O
style	O
sheets	O
.	O
</s>
<s>
HTML	B-Language
4	O
is	O
an	O
SGML	B-Language
application	O
conforming	O
to	O
ISO	B-Language
8879	I-Language
–	O
SGML	B-Language
.	O
</s>
<s>
April	O
24	O
,	O
1998	O
HTML	B-Language
4.0	I-Language
was	O
reissued	O
with	O
minor	O
edits	O
without	O
incrementing	O
the	O
version	O
number	O
.	O
</s>
<s>
December	O
24	O
,	O
1999	O
HTML	B-Language
4.01	I-Language
was	O
published	O
as	O
a	O
W3C	O
Recommendation	O
.	O
</s>
<s>
It	O
offers	O
the	O
same	O
three	O
variations	O
as	O
HTML	B-Language
4.0	I-Language
and	O
its	O
last	O
errata	O
were	O
published	O
on	O
May	O
12	O
,	O
2001	O
.	O
</s>
<s>
May	O
2000	O
ISO/IEC	O
15445:2000	O
(	O
"	O
ISO	O
HTML	B-Language
"	O
,	O
based	O
on	O
HTML	B-Language
4.01	I-Language
Strict	O
)	O
was	O
published	O
as	O
an	O
ISO/IEC	O
international	O
standard	O
.	O
</s>
<s>
After	O
HTML	B-Language
4.01	I-Language
,	O
there	O
were	O
no	O
new	O
versions	O
of	O
HTML	B-Language
for	O
many	O
years	O
,	O
as	O
the	O
development	O
of	O
the	O
parallel	O
,	O
XML-based	O
language	O
XHTML	B-Language
occupied	O
the	O
W3C	O
's	O
HTML	B-Language
Working	O
Group	O
.	O
</s>
<s>
October	O
28	O
,	O
2014	O
HTML5	B-Application
was	O
published	O
as	O
a	O
W3C	O
Recommendation	O
.	O
</s>
<s>
November	O
1	O
,	O
2016	O
HTML	B-Application
5.1	I-Application
was	O
published	O
as	O
a	O
W3C	O
Recommendation	O
.	O
</s>
<s>
December	O
14	O
,	O
2017	O
HTML	B-Application
5.2	I-Application
was	O
published	O
as	O
a	O
W3C	O
Recommendation	O
.	O
</s>
<s>
October	O
1991	O
HTML	B-General_Concept
Tags	I-General_Concept
,	O
an	O
informal	O
CERN	O
document	O
listing	O
18	O
HTML	B-General_Concept
tags	I-General_Concept
,	O
was	O
first	O
mentioned	O
in	O
public	O
.	O
</s>
<s>
June	O
1993	O
Hypertext	B-Language
Markup	I-Language
Language	I-Language
was	O
published	O
by	O
the	O
IETF	O
IIIR	O
Working	O
Group	O
as	O
an	O
Internet	O
Draft	O
(	O
a	O
rough	O
proposal	O
for	O
a	O
standard	O
)	O
.	O
</s>
<s>
November	O
1993	O
was	O
published	O
by	O
the	O
IETF	O
as	O
an	O
Internet	O
Draft	O
and	O
was	O
a	O
competing	O
proposal	O
to	O
the	O
Hypertext	B-Language
Markup	I-Language
Language	I-Language
draft	O
.	O
</s>
<s>
November	O
1994	O
First	O
draft	O
(	O
revision	O
00	O
)	O
of	O
HTML	B-Language
2.0	O
published	O
by	O
IETF	O
itself	O
(	O
called	O
as	O
"	O
HTML	B-Language
2.0	O
"	O
from	O
revision	O
02	O
)	O
,	O
that	O
finally	O
led	O
to	O
the	O
publication	O
of	O
in	O
November	O
1995	O
.	O
</s>
<s>
April	O
1995	O
(	O
authored	O
March	O
1995	O
)	O
HTML	B-Language
3.0	O
was	O
proposed	O
as	O
a	O
standard	O
to	O
the	O
IETF	O
,	O
but	O
the	O
proposal	O
expired	O
five	O
months	O
later	O
(	O
28	O
September	O
1995	O
)	O
without	O
further	O
action	O
.	O
</s>
<s>
It	O
included	O
many	O
of	O
the	O
capabilities	O
that	O
were	O
in	O
Raggett	O
's	O
HTML+	B-Language
proposal	O
,	O
such	O
as	O
support	O
for	O
tables	O
,	O
text	O
flow	O
around	O
figures	O
,	O
and	O
the	O
display	O
of	O
complex	O
mathematical	O
formulas	O
.	O
</s>
<s>
W3C	O
began	O
development	O
of	O
its	O
own	O
Arena	B-Application
browser	I-Application
as	O
a	O
test	O
bed	O
for	O
HTML	B-Language
3	O
and	O
Cascading	B-Language
Style	I-Language
Sheets	I-Language
,	O
but	O
HTML	B-Language
3.0	O
did	O
not	O
succeed	O
for	O
several	O
reasons	O
.	O
</s>
<s>
The	O
draft	O
was	O
considered	O
very	O
large	O
at	O
150	O
pages	O
and	O
the	O
pace	O
of	O
browser	B-Application
development	O
,	O
as	O
well	O
as	O
the	O
number	O
of	O
interested	O
parties	O
,	O
had	O
outstripped	O
the	O
resources	O
of	O
the	O
IETF	O
.	O
</s>
<s>
Browser	B-Application
vendors	O
,	O
including	O
Microsoft	O
and	O
Netscape	B-Protocol
at	O
the	O
time	O
,	O
chose	O
to	O
implement	O
different	O
subsets	O
of	O
HTML	B-Language
3	O
's	O
draft	O
features	O
as	O
well	O
as	O
to	O
introduce	O
their	O
own	O
extensions	O
to	O
it	O
.	O
</s>
<s>
(	O
see	O
Browser	B-Application
wars	I-Application
)	O
.	O
</s>
<s>
Dave	O
Raggett	O
,	O
who	O
has	O
been	O
a	O
W3C	O
Fellow	O
for	O
many	O
years	O
,	O
has	O
commented	O
for	O
example	O
:	O
"	O
To	O
a	O
certain	O
extent	O
,	O
Microsoft	O
built	O
its	O
business	O
on	O
the	O
Web	O
by	O
extending	O
HTML	B-Language
features.	O
"	O
</s>
<s>
January	O
2008	O
HTML5	B-Application
was	O
published	O
as	O
a	O
Working	O
Draft	O
by	O
the	O
W3C	O
.	O
</s>
<s>
Although	O
its	O
syntax	O
closely	O
resembles	O
that	O
of	O
SGML	B-Language
,	O
HTML5	B-Application
has	O
abandoned	O
any	O
attempt	O
to	O
be	O
an	O
SGML	B-Language
application	O
and	O
has	O
explicitly	O
defined	O
its	O
own	O
"	O
html	B-Language
"	O
serialization	O
,	O
in	O
addition	O
to	O
an	O
alternative	O
XML-based	O
XHTML5	O
serialization	O
.	O
</s>
<s>
On	O
14	O
February	O
2011	O
,	O
the	O
W3C	O
extended	O
the	O
charter	O
of	O
its	O
HTML	B-Language
Working	O
Group	O
with	O
clear	O
milestones	O
for	O
HTML5	B-Application
.	O
</s>
<s>
In	O
May	O
2011	O
,	O
the	O
working	O
group	O
advanced	O
HTML5	B-Application
to	O
"	O
Last	O
Call	O
"	O
,	O
an	O
invitation	O
to	O
communities	O
inside	O
and	O
outside	O
W3C	O
to	O
confirm	O
the	O
technical	O
soundness	O
of	O
the	O
specification	O
.	O
</s>
<s>
In	O
January	O
2011	O
,	O
the	O
WHATWG	B-Language
renamed	O
its	O
"	O
HTML5	B-Application
"	O
living	O
standard	O
to	O
"	O
HTML	B-Language
"	O
.	O
</s>
<s>
The	O
W3C	O
nevertheless	O
continues	O
its	O
project	O
to	O
release	O
HTML5	B-Application
.	O
</s>
<s>
In	O
July	O
2012	O
,	O
WHATWG	B-Language
and	O
W3C	O
decided	O
on	O
a	O
degree	O
of	O
separation	O
.	O
</s>
<s>
W3C	O
will	O
continue	O
the	O
HTML5	B-Application
specification	O
work	O
,	O
focusing	O
on	O
a	O
single	O
definitive	O
standard	O
,	O
which	O
is	O
considered	O
a	O
"	O
snapshot	O
"	O
by	O
WHATWG	B-Language
.	O
</s>
<s>
The	O
WHATWG	B-Language
organization	O
will	O
continue	O
its	O
work	O
with	O
HTML5	B-Application
as	O
a	O
"	O
Living	O
Standard	O
"	O
.	O
</s>
<s>
In	O
December	O
2012	O
,	O
W3C	O
designated	O
HTML5	B-Application
as	O
a	O
Candidate	O
Recommendation	O
.	O
</s>
<s>
In	O
September	O
2014	O
,	O
W3C	O
moved	O
HTML5	B-Application
to	O
Proposed	O
Recommendation	O
.	O
</s>
<s>
On	O
28	O
October	O
2014	O
,	O
HTML5	B-Application
was	O
released	O
as	O
a	O
stable	O
W3C	O
Recommendation	O
,	O
meaning	O
the	O
specification	O
process	O
is	O
complete	O
.	O
</s>
<s>
XHTML	B-Language
is	O
a	O
separate	O
language	O
that	O
began	O
as	O
a	O
reformulation	O
of	O
HTML	B-Language
4.01	I-Language
using	O
XML	B-Protocol
1.0	O
.	O
</s>
<s>
It	O
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
no	O
longer	O
being	O
developed	O
as	O
a	O
separate	O
standard	O
.	O
</s>
<s>
XHTML	B-Language
1.0	I-Language
was	O
published	O
as	O
a	O
W3C	O
Recommendation	O
on	O
January	O
26	O
,	O
2000	O
,	O
and	O
was	O
later	O
revised	O
and	O
republished	O
on	O
August	O
1	O
,	O
2002	O
.	O
</s>
<s>
It	O
offers	O
the	O
same	O
three	O
variations	O
as	O
HTML	B-Language
4.0	I-Language
and	O
4.01	O
,	O
reformulated	O
in	O
XML	B-Protocol
,	O
with	O
minor	O
restrictions	O
.	O
</s>
<s>
XHTML	B-Language
1.1	O
was	O
published	O
as	O
a	O
W3C	O
Recommendation	O
on	O
May	O
31	O
,	O
2001	O
.	O
</s>
<s>
It	O
is	O
based	O
on	O
XHTML	B-Language
1.0	I-Language
Strict	O
,	O
but	O
includes	O
minor	O
changes	O
,	O
can	O
be	O
customized	O
,	O
and	O
is	O
reformulated	O
using	O
modules	O
in	O
the	O
W3C	O
recommendation	O
"	O
Modularization	O
of	O
XHTML	B-Language
"	O
,	O
which	O
was	O
published	O
on	O
April	O
10	O
,	O
2001	O
.	O
</s>
<s>
XHTML	B-Language
2.0	O
was	O
a	O
working	O
draft	O
,	O
work	O
on	O
it	O
was	O
abandoned	O
in	O
2009	O
in	O
favor	O
of	O
work	O
on	O
HTML5	B-Application
and	O
XHTML5	O
.	O
</s>
<s>
XHTML	B-Language
2.0	O
was	O
incompatible	O
with	O
XHTML	B-Language
1.x	O
and	O
,	O
therefore	O
,	O
would	O
be	O
more	O
accurately	O
characterized	O
as	O
an	O
XHTML-inspired	O
new	O
language	O
than	O
an	O
update	O
to	O
XHTML	B-Language
1.x	O
.	O
</s>
<s>
On	O
28	O
May	O
2019	O
,	O
the	O
W3C	O
announced	O
that	O
WHATWG	B-Language
would	O
be	O
the	O
sole	O
publisher	O
of	O
the	O
HTML	B-Language
and	O
DOM	O
standards	O
.	O
</s>
<s>
The	O
W3C	O
and	O
WHATWG	B-Language
had	O
been	O
publishing	O
competing	O
standards	O
since	O
2012	O
.	O
</s>
<s>
While	O
the	O
W3C	O
standard	O
was	O
identical	O
to	O
the	O
WHATWG	B-Language
in	O
2007	O
the	O
standards	O
have	O
since	O
progressively	O
diverged	O
due	O
to	O
different	O
design	O
decisions	O
.	O
</s>
<s>
The	O
WHATWG	B-Language
"	O
Living	O
Standard	O
"	O
had	O
been	O
the	O
de	O
facto	O
web	O
standard	O
for	O
some	O
time	O
.	O
</s>
<s>
HTML	B-General_Concept
markup	I-General_Concept
consists	O
of	O
several	O
key	O
components	O
,	O
including	O
those	O
called	O
tags	B-General_Concept
(	O
and	O
their	O
attributes	O
)	O
,	O
character-based	O
data	O
types	O
,	O
character	O
references	O
and	O
entity	O
references	O
.	O
</s>
<s>
HTML	B-General_Concept
tags	I-General_Concept
most	O
commonly	O
come	O
in	O
pairs	O
like	O
and	O
,	O
although	O
some	O
represent	O
empty	O
elements	O
and	O
so	O
are	O
unpaired	O
,	O
for	O
example	O
.	O
</s>
<s>
The	O
first	O
tag	B-General_Concept
in	O
such	O
a	O
pair	O
is	O
the	O
start	O
tag	B-General_Concept
,	O
and	O
the	O
second	O
is	O
the	O
end	O
tag	B-General_Concept
(	O
they	O
are	O
also	O
called	O
opening	O
tags	B-General_Concept
and	O
closing	O
tags	B-General_Concept
)	O
.	O
</s>
<s>
Another	O
important	O
component	O
is	O
the	O
HTML	B-Language
document	O
type	O
declaration	O
,	O
which	O
triggers	O
standards	B-General_Concept
mode	I-General_Concept
rendering	O
.	O
</s>
<s>
The	O
markup	O
text	O
defines	O
the	O
browser	B-Application
page	O
title	O
shown	O
on	O
browser	B-Application
tabs	O
and	O
window	O
titles	O
and	O
the	O
tag	B-General_Concept
defines	O
a	O
division	O
of	O
the	O
page	O
used	O
for	O
easy	O
styling	O
.	O
</s>
<s>
The	O
Document	O
Type	O
Declaration	O
is	O
for	O
HTML5	B-Application
.	O
</s>
<s>
If	O
a	O
declaration	O
is	O
not	O
included	O
,	O
various	O
browsers	B-Application
will	O
revert	O
to	O
"	O
quirks	B-General_Concept
mode	I-General_Concept
"	O
for	O
rendering	O
.	O
</s>
<s>
HTML	B-Language
documents	O
imply	O
a	O
structure	O
of	O
nested	O
HTML	B-General_Concept
elements	I-General_Concept
.	O
</s>
<s>
These	O
are	O
indicated	O
in	O
the	O
document	O
by	O
HTML	B-General_Concept
tags	I-General_Concept
,	O
enclosed	O
in	O
angle	O
brackets	O
thus	O
:	O
.	O
</s>
<s>
In	O
the	O
simple	O
,	O
general	O
case	O
,	O
the	O
extent	O
of	O
an	O
element	O
is	O
indicated	O
by	O
a	O
pair	O
of	O
tags	B-General_Concept
:	O
a	O
"	O
start	O
tag	B-General_Concept
"	O
and	O
"	O
end	O
tag	B-General_Concept
"	O
.	O
</s>
<s>
The	O
text	O
content	O
of	O
the	O
element	O
,	O
if	O
any	O
,	O
is	O
placed	O
between	O
these	O
tags	B-General_Concept
.	O
</s>
<s>
Tags	B-General_Concept
may	O
also	O
enclose	O
further	O
tag	B-General_Concept
markup	O
between	O
the	O
start	O
and	O
end	O
,	O
including	O
a	O
mixture	O
of	O
tags	B-General_Concept
and	O
text	O
.	O
</s>
<s>
The	O
start	O
tag	B-General_Concept
may	O
also	O
include	O
the	O
element	O
's	O
attributes	O
within	O
the	O
tag	B-General_Concept
.	O
</s>
<s>
These	O
indicate	O
other	O
information	O
,	O
such	O
as	O
identifiers	O
for	O
sections	O
within	O
the	O
document	O
,	O
identifiers	O
used	O
to	O
bind	O
style	O
information	O
to	O
the	O
presentation	O
of	O
the	O
document	O
,	O
and	O
for	O
some	O
tags	B-General_Concept
such	O
as	O
the	O
used	O
to	O
embed	O
images	O
,	O
the	O
reference	O
to	O
the	O
image	O
resource	O
in	O
the	O
format	O
like	O
this	O
:	O
</s>
<s>
Some	O
elements	O
,	O
such	O
as	O
the	O
line	O
break	O
,	O
or	O
do	O
not	O
permit	O
any	O
embedded	O
content	O
,	O
either	O
text	O
or	O
further	O
tags	B-General_Concept
.	O
</s>
<s>
These	O
require	O
only	O
a	O
single	O
empty	O
tag	B-General_Concept
(	O
akin	O
to	O
a	O
start	O
tag	B-General_Concept
)	O
and	O
do	O
not	O
use	O
an	O
end	O
tag	B-General_Concept
.	O
</s>
<s>
Many	O
tags	B-General_Concept
,	O
particularly	O
the	O
closing	O
end	O
tag	B-General_Concept
for	O
the	O
very	O
commonly	O
used	O
paragraph	O
element	O
,	O
are	O
optional	O
.	O
</s>
<s>
An	O
HTML	B-Language
browser	B-Application
or	O
other	O
agent	O
can	O
infer	O
the	O
closure	O
for	O
the	O
end	O
of	O
an	O
element	O
from	O
the	O
context	O
and	O
the	O
structural	O
rules	O
defined	O
by	O
the	O
HTML	B-Language
standard	O
.	O
</s>
<s>
These	O
rules	O
are	O
complex	O
and	O
not	O
widely	O
understood	O
by	O
most	O
HTML	B-Language
coders	O
.	O
</s>
<s>
The	O
general	O
form	O
of	O
an	O
HTML	B-General_Concept
element	I-General_Concept
is	O
therefore	O
:	O
.	O
</s>
<s>
Some	O
HTML	B-General_Concept
elements	I-General_Concept
are	O
defined	O
as	O
empty	O
elements	O
and	O
take	O
the	O
form	O
.	O
</s>
<s>
Empty	O
elements	O
may	O
enclose	O
no	O
content	O
,	O
for	O
instance	O
,	O
the	O
tag	B-General_Concept
or	O
the	O
inline	O
tag	B-General_Concept
.	O
</s>
<s>
The	O
name	O
of	O
an	O
HTML	B-General_Concept
element	I-General_Concept
is	O
the	O
name	O
used	O
in	O
the	O
tags	B-General_Concept
.	O
</s>
<s>
Note	O
that	O
the	O
end	O
tag	B-General_Concept
's	O
name	O
is	O
preceded	O
by	O
a	O
slash	O
character	O
,	O
/	O
,	O
and	O
that	O
in	O
empty	O
elements	O
the	O
end	O
tag	B-General_Concept
is	O
neither	O
required	O
nor	O
allowed	O
.	O
</s>
<s>
Header	O
of	O
the	O
HTML	B-Language
document	O
:	O
.	O
</s>
<s>
HTML	B-Language
headings	O
are	O
defined	O
with	O
the	O
to	O
tags	B-General_Concept
with	O
H1	O
being	O
the	O
highest	O
(	O
or	O
most	O
important	O
)	O
level	O
and	O
H6	O
the	O
least	O
:	O
</s>
<s>
Note	O
that	O
CSS	B-Language
can	O
drastically	O
change	O
the	O
rendering	O
.	O
</s>
<s>
The	O
difference	O
between	O
and	O
is	O
that	O
breaks	O
a	O
line	O
without	O
altering	O
the	O
semantic	B-Application
structure	O
of	O
the	O
page	O
,	O
whereas	O
sections	O
the	O
page	O
into	O
paragraphs	O
.	O
</s>
<s>
The	O
element	O
is	O
an	O
empty	O
element	O
in	O
that	O
,	O
although	O
it	O
may	O
have	O
attributes	O
,	O
it	O
can	O
take	O
no	O
content	O
and	O
it	O
may	O
not	O
have	O
an	O
end	O
tag	B-General_Concept
.	O
</s>
<s>
This	O
is	O
a	O
link	O
in	O
HTML	B-Language
.	O
</s>
<s>
To	O
create	O
a	O
link	O
the	O
tag	B-General_Concept
is	O
used	O
.	O
</s>
<s>
There	O
are	O
several	O
types	O
of	O
markup	O
elements	O
used	O
in	O
HTML	B-Language
:	O
</s>
<s>
Structural	O
markup	O
does	O
not	O
denote	O
any	O
specific	O
rendering	O
,	O
but	O
most	O
web	B-Application
browsers	I-Application
have	O
default	O
styles	O
for	O
element	O
formatting	O
.	O
</s>
<s>
Content	O
may	O
be	O
further	O
styled	O
using	O
Cascading	B-Language
Style	I-Language
Sheets	I-Language
(	O
CSS	B-Language
)	O
.	O
</s>
<s>
Presentational	O
markup	O
indicates	O
the	O
appearance	O
of	O
the	O
text	O
,	O
regardless	O
of	O
its	O
purpose	O
For	O
example	O
,	O
indicates	O
that	O
visual	O
output	O
devices	O
should	O
render	B-Protocol
"	O
boldface	O
"	O
in	O
bold	O
text	O
,	O
but	O
gives	O
a	O
little	O
indication	O
what	O
devices	O
that	O
are	O
unable	O
to	O
do	O
this	O
(	O
such	O
as	O
aural	O
devices	O
that	O
read	O
the	O
text	O
aloud	O
)	O
should	O
do	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
both	O
and	O
,	O
there	O
are	O
other	O
elements	O
that	O
may	O
have	O
equivalent	O
visual	O
renderings	O
but	O
that	O
are	O
more	O
semantic	B-Application
in	O
nature	O
,	O
such	O
as	O
and	O
respectively	O
.	O
</s>
<s>
It	O
is	O
easier	O
to	O
see	O
how	O
an	O
aural	O
user	B-Protocol
agent	I-Protocol
should	O
interpret	O
the	O
latter	O
two	O
elements	O
.	O
</s>
<s>
Most	O
presentational	O
markup	O
elements	O
have	O
become	O
deprecated	B-General_Concept
under	O
the	O
HTML	B-Language
4.0	I-Language
specification	O
in	O
favor	O
of	O
using	O
CSS	B-Language
for	O
styling	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
HTML	B-General_Concept
markup	I-General_Concept
,	O
will	O
render	B-Protocol
the	O
word	O
"	O
Wikipedia	O
"	O
as	O
a	O
hyperlink	O
.	O
</s>
<s>
To	O
render	B-Protocol
an	O
image	O
as	O
a	O
hyperlink	O
,	O
an	O
img	O
element	O
is	O
inserted	O
as	O
content	O
into	O
the	O
a	O
element	O
.	O
</s>
<s>
Like	O
br	O
,	O
img	O
is	O
an	O
empty	O
element	O
with	O
attributes	O
but	O
no	O
content	O
or	O
closing	O
tag	B-General_Concept
.	O
</s>
<s>
Most	O
of	O
the	O
attributes	O
of	O
an	O
element	O
are	O
name	B-Application
–	I-Application
value	I-Application
pairs	I-Application
,	O
separated	O
by	O
=	O
and	O
written	O
within	O
the	O
start	O
tag	B-General_Concept
of	O
an	O
element	O
after	O
the	O
element	O
's	O
name	O
.	O
</s>
<s>
The	O
value	O
may	O
be	O
enclosed	O
in	O
single	O
or	O
double	O
quotes	O
,	O
although	O
values	O
consisting	O
of	O
certain	O
characters	O
can	O
be	O
left	O
unquoted	O
in	O
HTML	B-Language
(	O
but	O
not	O
XHTML	B-Language
)	O
.	O
</s>
<s>
In	O
contrast	O
with	O
name-value	B-Application
pair	I-Application
attributes	O
,	O
there	O
are	O
some	O
attributes	O
that	O
affect	O
the	O
element	O
simply	O
by	O
their	O
presence	O
in	O
the	O
start	O
tag	B-General_Concept
of	O
the	O
element	O
,	O
like	O
the	O
ismap	O
attribute	O
for	O
the	O
img	O
element	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
ID	O
"	O
Attributes	O
"	O
in	O
https://en.wikipedia.org/wiki/HTML#Attributes	O
.	O
</s>
<s>
This	O
can	O
be	O
used	O
for	O
semantic	B-Application
or	O
presentation	O
purposes	O
.	O
</s>
<s>
For	O
example	O
,	O
an	O
HTML	B-Language
document	O
might	O
semantically	O
use	O
the	O
designation	O
to	O
indicate	O
that	O
all	O
elements	O
with	O
this	O
class	O
value	O
are	O
subordinate	O
to	O
the	O
main	O
text	O
of	O
the	O
document	O
.	O
</s>
<s>
In	O
presentation	O
,	O
such	O
elements	O
might	O
be	O
gathered	O
together	O
and	O
presented	O
as	O
footnotes	O
on	O
a	O
page	O
instead	O
of	O
appearing	O
in	O
the	O
place	O
where	O
they	O
occur	O
in	O
the	O
HTML	B-Language
source	O
.	O
</s>
<s>
Class	O
attributes	O
are	O
used	O
semantically	O
in	O
microformats	B-General_Concept
.	O
</s>
<s>
It	O
is	O
considered	O
better	O
practice	O
to	O
use	O
an	O
element	O
's	O
id	O
or	O
class	O
attributes	O
to	O
select	O
the	O
element	O
from	O
within	O
a	O
stylesheet	B-Language
,	O
though	O
sometimes	O
this	O
can	O
be	O
too	O
cumbersome	O
for	O
a	O
simple	O
,	O
specific	O
,	O
or	O
ad	O
hoc	O
styling	O
.	O
</s>
<s>
In	O
most	O
browsers	B-Application
this	O
attribute	O
is	O
displayed	O
as	O
a	O
tooltip	O
.	O
</s>
<s>
This	O
example	O
displays	O
as	O
HTML	B-Language
;	O
in	O
most	O
browsers	B-Application
,	O
pointing	O
the	O
cursor	O
at	O
the	O
abbreviation	O
should	O
display	O
the	O
title	O
text	O
"	O
Hypertext	O
Markup	O
Language.	O
"	O
</s>
<s>
As	O
of	O
version	O
4.0	O
,	O
HTML	B-Language
defines	O
a	O
set	O
of	O
252	O
character	B-General_Concept
entity	I-General_Concept
references	I-General_Concept
and	O
a	O
set	O
of	O
1,114,050	O
numeric	B-General_Concept
character	I-General_Concept
references	I-General_Concept
,	O
both	O
of	O
which	O
allow	O
individual	O
characters	O
to	O
be	O
written	O
via	O
simple	O
markup	O
,	O
rather	O
than	O
literally	O
.	O
</s>
<s>
The	O
ability	O
to	O
"	O
escape	B-Algorithm
"	O
characters	O
in	O
this	O
way	O
allows	O
for	O
the	O
characters	O
<	O
and	O
&	O
(	O
when	O
written	O
as	O
<	O
and	O
&	O
,	O
respectively	O
)	O
to	O
be	O
interpreted	O
as	O
character	O
data	O
,	O
rather	O
than	O
markup	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
literal	O
<	O
normally	O
indicates	O
the	O
start	O
of	O
a	O
tag	B-General_Concept
,	O
and	O
&	O
normally	O
indicates	O
the	O
start	O
of	O
a	O
character	B-General_Concept
entity	I-General_Concept
reference	I-General_Concept
or	O
numeric	B-General_Concept
character	I-General_Concept
reference	I-General_Concept
;	O
writing	O
it	O
as	O
&	O
or	O
&	O
or	O
&	O
allows	O
&	O
to	O
be	O
included	O
in	O
the	O
content	O
of	O
an	O
element	O
or	O
in	O
the	O
value	O
of	O
an	O
attribute	O
.	O
</s>
<s>
Equivalently	O
,	O
the	O
single-quote	O
character	O
( 	O
 '	O
)	O
,	O
when	O
not	O
used	O
to	O
quote	O
an	O
attribute	O
value	O
,	O
must	O
also	O
be	O
escaped	O
as	O
'	O
or	O
'	O
(	O
or	O
as	O
'	O
in	O
HTML5	B-Application
or	O
XHTML	B-Language
documents	O
)	O
when	O
it	O
appears	O
within	O
the	O
attribute	O
value	O
itself	O
.	O
</s>
<s>
If	O
document	O
authors	O
overlook	O
the	O
need	O
to	O
escape	B-Algorithm
such	O
characters	O
,	O
some	O
browsers	B-Application
can	O
be	O
very	O
forgiving	O
and	O
try	O
to	O
use	O
context	O
to	O
guess	O
their	O
intent	O
.	O
</s>
<s>
The	O
result	O
is	O
still	O
invalid	O
markup	O
,	O
which	O
makes	O
the	O
document	O
less	O
accessible	O
to	O
other	O
browsers	B-Application
and	O
to	O
other	O
user	B-Protocol
agents	I-Protocol
that	O
may	O
try	O
to	O
parse	O
the	O
document	O
for	O
search	B-Application
and	I-Application
indexing	I-Application
purposes	O
for	O
example	O
.	O
</s>
<s>
Escaping	O
also	O
allows	O
for	O
characters	O
that	O
are	O
not	O
easily	O
typed	O
,	O
or	O
that	O
are	O
not	O
available	O
in	O
the	O
document	O
's	O
character	B-General_Concept
encoding	I-General_Concept
,	O
to	O
be	O
represented	O
within	O
the	O
element	O
and	O
attribute	O
content	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
acute-accented	O
e	O
( é	O
)	O
,	O
a	O
character	O
typically	O
found	O
only	O
on	O
Western	O
European	O
and	O
South	O
American	O
keyboards	O
,	O
can	O
be	O
written	O
in	O
any	O
HTML	B-Language
document	O
as	O
the	O
entity	O
reference	O
é	O
or	O
as	O
the	O
numeric	O
references	O
é	O
or	O
é	O
,	O
using	O
characters	O
that	O
are	O
available	O
on	O
all	O
keyboards	O
and	O
are	O
supported	O
in	O
all	O
character	B-General_Concept
encodings	I-General_Concept
.	O
</s>
<s>
Unicode	O
character	B-General_Concept
encodings	I-General_Concept
such	O
as	O
UTF-8	O
are	O
compatible	O
with	O
all	O
modern	O
browsers	B-Application
and	O
allow	O
direct	O
access	O
to	O
almost	O
all	O
the	O
characters	O
of	O
the	O
world	O
's	O
writing	O
systems	O
.	O
</s>
<s>
HTML	B-Language
defines	O
several	O
data	O
types	O
for	O
element	O
content	O
,	O
such	O
as	O
script	O
data	O
and	O
stylesheet	B-Language
data	O
,	O
and	O
a	O
plethora	O
of	O
types	O
for	O
attribute	O
values	O
,	O
including	O
IDs	O
,	O
names	O
,	O
URIs	O
,	O
numbers	O
,	O
units	O
of	O
length	O
,	O
languages	O
,	O
media	O
descriptors	O
,	O
colors	O
,	O
character	B-General_Concept
encodings	I-General_Concept
,	O
dates	O
and	O
times	O
,	O
and	O
so	O
on	O
.	O
</s>
<s>
HTML	B-Language
documents	O
are	O
required	O
to	O
start	O
with	O
a	O
Document	O
Type	O
Declaration	O
(	O
informally	O
,	O
a	O
"	O
doctype	O
"	O
)	O
.	O
</s>
<s>
In	O
browsers	B-Application
,	O
the	O
doctype	O
helps	O
to	O
define	O
the	O
rendering	O
mode	O
—	O
particularly	O
whether	O
to	O
use	O
quirks	B-General_Concept
mode	I-General_Concept
.	O
</s>
<s>
The	O
original	O
purpose	O
of	O
the	O
doctype	O
was	O
to	O
enable	O
the	O
parsing	O
and	O
validation	O
of	O
HTML	B-Language
documents	O
by	O
SGML	B-Language
tools	O
based	O
on	O
the	O
Document	B-Language
Type	I-Language
Definition	I-Language
(	O
DTD	O
)	O
.	O
</s>
<s>
Browsers	B-Application
,	O
on	O
the	O
other	O
hand	O
,	O
do	O
not	O
implement	O
HTML	B-Language
as	O
an	O
application	O
of	O
SGML	B-Language
and	O
as	O
consequence	O
do	O
not	O
read	O
the	O
DTD	O
.	O
</s>
<s>
HTML5	B-Application
does	O
not	O
define	O
a	O
DTD	O
;	O
therefore	O
,	O
in	O
HTML5	B-Application
the	O
doctype	O
declaration	O
is	O
simpler	O
and	O
shorter	O
:	O
</s>
<s>
This	O
declaration	O
references	O
the	O
DTD	O
for	O
the	O
"	O
strict	O
"	O
version	O
of	O
HTML	B-Language
4.01	I-Language
.	O
</s>
<s>
SGML-based	O
validators	O
read	O
the	O
DTD	O
in	O
order	O
to	O
properly	O
parse	O
the	O
document	O
and	O
to	O
perform	O
validation	O
.	O
</s>
<s>
In	O
modern	O
browsers	B-Application
,	O
a	O
valid	O
doctype	O
activates	O
standards	B-General_Concept
mode	I-General_Concept
as	O
opposed	O
to	O
quirks	B-General_Concept
mode	I-General_Concept
.	O
</s>
<s>
In	O
addition	O
,	O
HTML	B-Language
4.01	I-Language
provides	O
Transitional	O
and	O
Frameset	B-General_Concept
DTDs	O
,	O
as	O
explained	O
below	O
.	O
</s>
<s>
The	O
transitional	O
type	O
is	O
the	O
most	O
inclusive	O
,	O
incorporating	O
current	O
tags	B-General_Concept
as	O
well	O
as	O
older	O
or	O
"	O
deprecated	B-General_Concept
"	O
tags	B-General_Concept
,	O
with	O
the	O
Strict	O
DTD	O
excluding	O
deprecated	B-General_Concept
tags	B-General_Concept
.	O
</s>
<s>
The	O
frameset	B-General_Concept
has	O
all	O
tags	B-General_Concept
necessary	O
to	O
make	O
frames	O
on	O
a	O
page	O
along	O
with	O
the	O
tags	B-General_Concept
included	O
in	O
transitional	O
type	O
.	O
</s>
<s>
Semantic	B-General_Concept
HTML	I-General_Concept
is	O
a	O
way	O
of	O
writing	O
HTML	B-Language
that	O
emphasizes	O
the	O
meaning	O
of	O
the	O
encoded	O
information	O
over	O
its	O
presentation	O
(	O
look	O
)	O
.	O
</s>
<s>
HTML	B-Language
has	O
included	O
semantic	B-General_Concept
markup	I-General_Concept
from	O
its	O
inception	O
,	O
but	O
has	O
also	O
included	O
presentational	O
markup	O
,	O
such	O
as	O
,	O
and	O
tags	B-General_Concept
.	O
</s>
<s>
There	O
are	O
also	O
the	O
semantically	O
neutral	O
div	B-General_Concept
and	I-General_Concept
span	I-General_Concept
tags	B-General_Concept
.	O
</s>
<s>
Since	O
the	O
late	O
1990s	O
,	O
when	O
Cascading	B-Language
Style	I-Language
Sheets	I-Language
were	O
beginning	O
to	O
work	O
in	O
most	O
browsers	B-Application
,	O
web	O
authors	O
have	O
been	O
encouraged	O
to	O
avoid	O
the	O
use	O
of	O
presentational	O
HTML	B-General_Concept
markup	I-General_Concept
with	O
a	O
view	O
to	O
the	O
separation	O
of	O
content	O
and	O
presentation	O
.	O
</s>
<s>
In	O
a	O
2001	O
discussion	O
of	O
the	O
Semantic	B-Application
Web	O
,	O
Tim	O
Berners-Lee	O
and	O
others	O
gave	O
examples	O
of	O
ways	O
in	O
which	O
intelligent	O
software	O
"	O
agents	O
"	O
may	O
one	O
day	O
automatically	O
crawl	O
the	O
web	O
and	O
find	O
,	O
filter	O
,	O
and	O
correlate	O
previously	O
unrelated	O
,	O
published	O
facts	O
for	O
the	O
benefit	O
of	O
human	O
users	O
.	O
</s>
<s>
Such	O
agents	O
are	O
not	O
commonplace	O
even	O
now	O
,	O
but	O
some	O
of	O
the	O
ideas	O
of	O
Web	O
2.0	O
,	O
mashups	B-Application
and	O
price	O
comparison	O
websites	O
may	O
be	O
coming	O
close	O
.	O
</s>
<s>
The	O
main	O
difference	O
between	O
these	O
web	O
application	O
hybrids	O
and	O
Berners-Lee	O
'	O
s	O
semantic	B-Application
agents	O
lies	O
in	O
the	O
fact	O
that	O
the	O
current	O
aggregation	B-Application
and	O
hybridization	O
of	O
information	O
is	O
usually	O
designed	O
by	O
web	B-Operating_System
developers	I-Operating_System
,	O
who	O
already	O
know	O
the	O
web	O
locations	O
and	O
the	O
API	B-Application
semantics	I-Application
of	O
the	O
specific	O
data	O
they	O
wish	O
to	O
mash	O
,	O
compare	O
and	O
combine	O
.	O
</s>
<s>
An	O
important	O
type	O
of	O
web	B-Protocol
agent	I-Protocol
that	O
does	O
crawl	O
and	O
read	O
web	O
pages	O
automatically	O
,	O
without	O
prior	O
knowledge	O
of	O
what	O
it	O
might	O
find	O
,	O
is	O
the	O
web	B-Application
crawler	I-Application
or	O
search-engine	B-Application
spider	I-Application
.	O
</s>
<s>
These	O
software	O
agents	O
are	O
dependent	O
on	O
the	O
semantic	B-Application
clarity	O
of	O
web	O
pages	O
they	O
find	O
as	O
they	O
use	O
various	O
techniques	O
and	O
algorithms	O
to	O
read	O
and	O
index	O
millions	O
of	O
web	O
pages	O
a	O
day	O
and	O
provide	O
web	O
users	O
with	O
search	B-Application
facilities	I-Application
without	O
which	O
the	O
World	O
Wide	O
Web	O
's	O
usefulness	O
would	O
be	O
greatly	O
reduced	O
.	O
</s>
<s>
In	O
order	O
for	O
search	B-Application
engine	I-Application
spiders	I-Application
to	O
be	O
able	O
to	O
rate	O
the	O
significance	O
of	O
pieces	O
of	O
text	O
they	O
find	O
in	O
HTML	B-Language
documents	O
,	O
and	O
also	O
for	O
those	O
creating	O
mashups	B-Application
and	O
other	O
hybrids	O
as	O
well	O
as	O
for	O
more	O
automated	B-Application
agents	I-Application
as	O
they	O
are	O
developed	O
,	O
the	O
semantic	B-Application
structures	O
that	O
exist	O
in	O
HTML	B-Language
need	O
to	O
be	O
widely	O
and	O
uniformly	O
applied	O
to	O
bring	O
out	O
the	O
meaning	O
of	O
the	O
published	O
text	O
.	O
</s>
<s>
Presentational	O
markup	O
tags	B-General_Concept
are	O
deprecated	B-General_Concept
in	O
current	O
HTML	B-Language
and	O
XHTML	B-Language
recommendations	O
.	O
</s>
<s>
The	O
majority	O
of	O
presentational	O
features	O
from	O
previous	O
versions	O
of	O
HTML	B-Language
are	O
no	O
longer	O
allowed	O
as	O
they	O
lead	O
to	O
poorer	O
accessibility	O
,	O
higher	O
cost	O
of	O
site	O
maintenance	O
,	O
and	O
larger	O
document	O
sizes	O
.	O
</s>
<s>
Good	O
semantic	B-General_Concept
HTML	I-General_Concept
also	O
improves	O
the	O
accessibility	O
of	O
web	O
documents	O
(	O
see	O
also	O
Web	O
Content	O
Accessibility	O
Guidelines	O
)	O
.	O
</s>
<s>
For	O
example	O
,	O
when	O
a	O
screen	O
reader	O
or	O
audio	O
browser	B-Application
can	O
correctly	O
ascertain	O
the	O
structure	O
of	O
a	O
document	O
,	O
it	O
will	O
not	O
waste	O
the	O
visually	O
impaired	O
user	O
's	O
time	O
by	O
reading	O
out	O
repeated	O
or	O
irrelevant	O
information	O
when	O
it	O
has	O
been	O
marked	O
up	O
correctly	O
.	O
</s>
<s>
HTML	B-Language
documents	O
can	O
be	O
delivered	O
by	O
the	O
same	O
means	O
as	O
any	O
other	O
computer	B-Operating_System
file	I-Operating_System
.	O
</s>
<s>
However	O
,	O
they	O
are	O
most	O
often	O
delivered	O
either	O
by	O
HTTP	B-Protocol
from	O
a	O
web	B-Application
server	I-Application
or	O
by	O
email	O
.	O
</s>
<s>
The	O
World	O
Wide	O
Web	O
is	O
composed	O
primarily	O
of	O
HTML	B-Language
documents	O
transmitted	O
from	O
web	B-Application
servers	I-Application
to	O
web	B-Application
browsers	I-Application
using	O
the	O
Hypertext	B-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
(	O
HTTP	B-Protocol
)	O
.	O
</s>
<s>
However	O
,	O
HTTP	B-Protocol
is	O
used	O
to	O
serve	O
images	O
,	O
sound	O
,	O
and	O
other	O
content	O
,	O
in	O
addition	O
to	O
HTML	B-Language
.	O
</s>
<s>
To	O
allow	O
the	O
web	B-Application
browser	I-Application
to	O
know	O
how	O
to	O
handle	O
each	O
document	O
it	O
receives	O
,	O
other	O
information	O
is	O
transmitted	O
along	O
with	O
the	O
document	O
.	O
</s>
<s>
This	O
meta	O
data	O
usually	O
includes	O
the	O
MIME	B-Application
type	I-Application
(	O
e.g.	O
,	O
text/html	B-Language
or	O
application/xhtml	O
+xml	O
)	O
and	O
the	O
character	B-General_Concept
encoding	I-General_Concept
(	O
see	O
Character	B-General_Concept
encoding	I-General_Concept
in	I-General_Concept
HTML	I-General_Concept
)	O
.	O
</s>
<s>
In	O
modern	O
browsers	B-Application
,	O
the	O
MIME	B-Application
type	I-Application
that	O
is	O
sent	O
with	O
the	O
HTML	B-Language
document	O
may	O
affect	O
how	O
the	O
document	O
is	O
initially	O
interpreted	O
.	O
</s>
<s>
A	O
document	O
sent	O
with	O
the	O
XHTML	B-Language
MIME	B-Application
type	I-Application
is	O
expected	O
to	O
be	O
well-formed	B-Language
XML	I-Language
;	O
syntax	O
errors	O
may	O
cause	O
the	O
browser	B-Application
to	O
fail	O
to	O
render	B-Protocol
it	O
.	O
</s>
<s>
The	O
same	O
document	O
sent	O
with	O
the	O
HTML	B-Language
MIME	B-Application
type	I-Application
might	O
be	O
displayed	O
successfully	O
since	O
some	O
browsers	B-Application
are	O
more	O
lenient	O
with	O
HTML	B-Language
.	O
</s>
<s>
The	O
W3C	O
recommendations	O
state	O
that	O
XHTML	B-Language
1.0	I-Language
documents	O
that	O
follow	O
guidelines	O
set	O
forth	O
in	O
the	O
recommendation	O
's	O
Appendix	O
C	O
may	O
be	O
labeled	O
with	O
either	O
MIME	B-Application
Type	I-Application
.	O
</s>
<s>
XHTML	B-Language
1.1	O
also	O
states	O
that	O
XHTML	B-Language
1.1	O
documents	O
should	O
be	O
labeled	O
with	O
either	O
MIME	B-Application
type	I-Application
.	O
</s>
<s>
Most	O
graphical	O
email	O
clients	O
allow	O
the	O
use	O
of	O
a	O
subset	O
of	O
HTML	B-Language
(	O
often	O
ill-defined	O
)	O
to	O
provide	O
formatting	O
and	O
semantic	B-General_Concept
markup	I-General_Concept
not	O
available	O
with	O
plain	O
text	O
.	O
</s>
<s>
Many	O
such	O
clients	O
include	O
both	O
a	O
GUI	B-Application
editor	O
for	O
composing	O
HTML	B-Language
e-mail	O
messages	O
and	O
a	O
rendering	O
engine	O
for	O
displaying	O
them	O
.	O
</s>
<s>
Use	O
of	O
HTML	B-Language
in	O
e-mail	O
is	O
criticized	O
by	O
some	O
because	O
of	O
compatibility	O
issues	O
,	O
because	O
it	O
can	O
help	O
disguise	O
phishing	O
attacks	O
,	O
because	O
of	O
accessibility	O
issues	O
for	O
blind	O
or	O
visually	O
impaired	O
people	O
,	O
because	O
it	O
can	O
confuse	O
spam	O
filters	O
and	O
because	O
the	O
message	O
size	O
is	O
larger	O
than	O
plain	O
text	O
.	O
</s>
<s>
The	O
most	O
common	O
filename	O
extension	O
for	O
files	B-Operating_System
containing	O
HTML	B-Language
is	O
.html	B-Language
.	O
</s>
<s>
A	O
common	O
abbreviation	O
of	O
this	O
is	O
.htm	B-Language
,	O
which	O
originated	O
because	O
some	O
early	O
operating	O
systems	O
and	O
file	O
systems	O
,	O
such	O
as	O
DOS	B-Device
and	O
the	O
limitations	O
imposed	O
by	O
FAT	B-Application
data	O
structure	O
,	O
limited	O
file	O
extensions	O
to	O
three	O
letters	O
.	O
</s>
<s>
An	O
HTML	B-Language
Application	O
(	O
HTA	O
;	O
file	O
extension	O
.hta	O
)	O
is	O
a	O
Microsoft	B-Application
Windows	I-Application
application	O
that	O
uses	O
HTML	B-Language
and	O
Dynamic	O
HTML	B-Language
in	O
a	O
browser	B-Application
to	O
provide	O
the	O
application	O
's	O
graphical	B-Application
interface	I-Application
.	O
</s>
<s>
A	O
regular	O
HTML	B-Language
file	I-Language
is	O
confined	O
to	O
the	O
security	O
model	O
of	O
the	O
web	B-Protocol
browser	I-Protocol
's	I-Protocol
security	I-Protocol
,	O
communicating	O
only	O
to	O
web	B-Application
servers	I-Application
and	O
manipulating	O
only	O
web	O
page	O
objects	O
and	O
site	B-Application
cookies	I-Application
.	O
</s>
<s>
An	O
HTA	O
runs	O
as	O
a	O
fully	O
trusted	O
application	O
and	O
therefore	O
has	O
more	O
privileges	O
,	O
like	O
creation/editing/removal	O
of	O
files	B-Operating_System
and	O
Windows	B-Protocol
Registry	I-Protocol
entries	O
.	O
</s>
<s>
Because	O
they	O
operate	O
outside	O
the	O
browser	B-Application
's	O
security	O
model	O
,	O
HTAs	O
cannot	O
be	O
executed	O
via	O
HTTP	B-Protocol
,	O
but	O
must	O
be	O
downloaded	O
(	O
just	O
like	O
an	O
EXE	O
file	O
)	O
and	O
executed	O
from	O
local	O
file	O
system	O
.	O
</s>
<s>
Since	O
its	O
inception	O
,	O
HTML	B-Language
and	O
its	O
associated	O
protocols	O
gained	O
acceptance	O
relatively	O
quickly	O
.	O
</s>
<s>
Though	O
its	O
creators	O
originally	O
conceived	O
of	O
HTML	B-Language
as	O
a	O
semantic	B-Application
language	O
devoid	O
of	O
presentation	O
details	O
,	O
practical	O
uses	O
pushed	O
many	O
presentational	O
elements	O
and	O
attributes	O
into	O
the	O
language	O
,	O
driven	O
largely	O
by	O
the	O
various	O
browser	B-Application
vendors	O
.	O
</s>
<s>
The	O
latest	O
standards	O
surrounding	O
HTML	B-Language
reflect	O
efforts	O
to	O
overcome	O
the	O
sometimes	O
chaotic	O
development	O
of	O
the	O
language	O
and	O
to	O
create	O
a	O
rational	O
foundation	O
for	O
building	O
both	O
meaningful	O
and	O
well-presented	O
documents	O
.	O
</s>
<s>
To	O
return	O
HTML	B-Language
to	O
its	O
role	O
as	O
a	O
semantic	B-Application
language	O
,	O
the	O
W3C	O
has	O
developed	O
style	O
languages	O
such	O
as	O
CSS	B-Language
and	O
XSL	B-Language
to	O
shoulder	O
the	O
burden	O
of	O
presentation	O
.	O
</s>
<s>
In	O
conjunction	O
,	O
the	O
HTML	B-Language
specification	O
has	O
slowly	O
reined	O
in	O
the	O
presentational	O
elements	O
.	O
</s>
<s>
There	O
are	O
two	O
axes	O
differentiating	O
various	O
variations	O
of	O
HTML	B-Language
as	O
currently	O
specified	O
:	O
SGML-based	O
HTML	B-Language
versus	O
XML-based	O
HTML	B-Language
(	O
referred	O
to	O
as	O
XHTML	B-Language
)	O
on	O
one	O
axis	O
,	O
and	O
strict	O
versus	O
transitional	O
(	O
loose	O
)	O
versus	O
frameset	B-General_Concept
on	O
the	O
other	O
axis	O
.	O
</s>
<s>
One	O
difference	O
in	O
the	O
latest	O
HTML	B-Language
specifications	O
lies	O
in	O
the	O
distinction	O
between	O
the	O
SGML-based	O
specification	O
and	O
the	O
XML-based	O
specification	O
.	O
</s>
<s>
The	O
XML-based	O
specification	O
is	O
usually	O
called	O
XHTML	B-Language
to	O
distinguish	O
it	O
clearly	O
from	O
the	O
more	O
traditional	O
definition	O
.	O
</s>
<s>
However	O
,	O
the	O
root	O
element	O
name	O
continues	O
to	O
be	O
"	O
html	B-Language
"	O
even	O
in	O
the	O
XHTML-specified	O
HTML	B-Language
.	O
</s>
<s>
The	O
W3C	O
intended	O
XHTML	B-Language
1.0	I-Language
to	O
be	O
identical	O
to	O
HTML	B-Language
4.01	I-Language
except	O
where	O
limitations	O
of	O
XML	B-Protocol
over	O
the	O
more	O
complex	O
SGML	B-Language
require	O
workarounds	O
.	O
</s>
<s>
Because	O
XHTML	B-Language
and	O
HTML	B-Language
are	O
closely	O
related	O
,	O
they	O
are	O
sometimes	O
documented	O
in	O
parallel	O
.	O
</s>
<s>
In	O
such	O
circumstances	O
,	O
some	O
authors	O
conflate	O
the	O
two	O
names	O
as	O
(	O
X	O
)	O
HTML	B-Language
or	O
X(HTML )	O
.	O
</s>
<s>
Like	O
HTML	B-Language
4.01	I-Language
,	O
XHTML	B-Language
1.0	I-Language
has	O
three	O
sub-specifications	O
:	O
strict	O
,	O
transitional	O
,	O
and	O
frameset	B-General_Concept
.	O
</s>
<s>
Aside	O
from	O
the	O
different	O
opening	O
declarations	O
for	O
a	O
document	O
,	O
the	O
differences	O
between	O
an	O
HTML	B-Language
4.01	I-Language
and	O
XHTML	B-Language
1.0	I-Language
document	O
—	O
in	O
each	O
of	O
the	O
corresponding	O
DTDs	O
—	O
are	O
largely	O
syntactic	O
.	O
</s>
<s>
The	O
underlying	O
syntax	O
of	O
HTML	B-Language
allows	O
many	O
shortcuts	O
that	O
XHTML	B-Language
does	O
not	O
,	O
such	O
as	O
elements	O
with	O
optional	O
opening	O
or	O
closing	O
tags	B-General_Concept
,	O
and	O
even	O
empty	O
elements	O
which	O
must	O
not	O
have	O
an	O
end	O
tag	B-General_Concept
.	O
</s>
<s>
By	O
contrast	O
,	O
XHTML	B-Language
requires	O
all	O
elements	O
to	O
have	O
an	O
opening	O
tag	B-General_Concept
and	O
a	O
closing	O
tag	B-General_Concept
.	O
</s>
<s>
XHTML	B-Language
,	O
however	O
,	O
also	O
introduces	O
a	O
new	O
shortcut	O
:	O
an	O
XHTML	B-Language
tag	B-General_Concept
may	O
be	O
opened	O
and	O
closed	O
within	O
the	O
same	O
tag	B-General_Concept
,	O
by	O
including	O
a	O
slash	O
before	O
the	O
end	O
of	O
the	O
tag	B-General_Concept
like	O
this	O
:	O
.	O
</s>
<s>
The	O
introduction	O
of	O
this	O
shorthand	O
,	O
which	O
is	O
not	O
used	O
in	O
the	O
SGML	B-Language
declaration	O
for	O
HTML	B-Language
4.01	I-Language
,	O
may	O
confuse	O
earlier	O
software	O
unfamiliar	O
with	O
this	O
new	O
convention	O
.	O
</s>
<s>
A	O
fix	O
for	O
this	O
is	O
to	O
include	O
a	O
space	O
before	O
closing	O
the	O
tag	B-General_Concept
,	O
as	O
such	O
:	O
.	O
</s>
<s>
To	O
understand	O
the	O
subtle	O
differences	O
between	O
HTML	B-Language
and	O
XHTML	B-Language
,	O
consider	O
the	O
transformation	O
of	O
a	O
valid	O
and	O
well-formed	B-Language
XHTML	B-Language
1.0	I-Language
document	O
that	O
adheres	O
to	O
Appendix	O
C	O
(	O
see	O
below	O
)	O
into	O
a	O
valid	O
HTML	B-Language
4.01	I-Language
document	O
.	O
</s>
<s>
The	O
language	O
for	O
an	O
element	O
should	O
be	O
specified	O
with	O
a	O
lang	O
attribute	O
rather	O
than	O
the	O
XHTML	B-Language
xml:lang	B-Protocol
attribute	O
.	O
</s>
<s>
XHTML	B-Language
uses	O
XML	B-Protocol
's	O
built-in	O
language-defining	O
functionality	O
attribute	O
.	O
</s>
<s>
Remove	O
the	O
XML	B-Protocol
namespace	O
(	O
xmlns	O
=	O
URI	O
)	O
.	O
</s>
<s>
HTML	B-Language
has	O
no	O
facilities	O
for	O
namespaces	O
.	O
</s>
<s>
Change	O
the	O
document	O
type	O
declaration	O
from	O
XHTML	B-Language
1.0	I-Language
to	O
HTML	B-Language
4.01	I-Language
.	O
</s>
<s>
If	O
present	O
,	O
remove	O
the	O
XML	B-Protocol
declaration	O
.	O
</s>
<s>
Ensure	O
that	O
the	O
document	O
's	O
MIME	B-Application
type	I-Application
is	O
set	O
to	O
text/html	B-Language
.	O
</s>
<s>
For	O
both	O
HTML	B-Language
and	O
XHTML	B-Language
,	O
this	O
comes	O
from	O
the	O
HTTP	B-Protocol
Content-Type	B-Application
header	O
sent	O
by	O
the	O
server	O
.	O
</s>
<s>
Change	O
the	O
XML	B-Protocol
empty-element	O
syntax	O
to	O
an	O
HTML	B-Language
style	O
empty	O
element	O
(	O
to	O
)	O
.	O
</s>
<s>
Those	O
are	O
the	O
main	O
changes	O
necessary	O
to	O
translate	O
a	O
document	O
from	O
XHTML	B-Language
1.0	I-Language
to	O
HTML	B-Language
4.01	I-Language
.	O
</s>
<s>
To	O
translate	O
from	O
HTML	B-Language
to	O
XHTML	B-Language
would	O
also	O
require	O
the	O
addition	O
of	O
any	O
omitted	O
opening	O
or	O
closing	O
tags	B-General_Concept
.	O
</s>
<s>
Whether	O
coding	O
in	O
HTML	B-Language
or	O
XHTML	B-Language
it	O
may	O
just	O
be	O
best	O
to	O
always	O
include	O
the	O
optional	O
tags	B-General_Concept
within	O
an	O
HTML	B-Language
document	O
rather	O
than	O
remembering	O
which	O
tags	B-General_Concept
can	O
be	O
omitted	O
.	O
</s>
<s>
A	O
well-formed	B-Language
XHTML	B-Language
document	O
adheres	O
to	O
all	O
the	O
syntax	O
requirements	O
of	O
XML	B-Protocol
.	O
</s>
<s>
A	O
valid	O
document	O
adheres	O
to	O
the	O
content	O
specification	O
for	O
XHTML	B-Language
,	O
which	O
describes	O
the	O
document	O
structure	O
.	O
</s>
<s>
The	O
W3C	O
recommends	O
several	O
conventions	O
to	O
ensure	O
an	O
easy	O
migration	O
between	O
HTML	B-Language
and	O
XHTML	B-Language
(	O
see	O
)	O
.	O
</s>
<s>
The	O
following	O
steps	O
can	O
be	O
applied	O
to	O
XHTML	B-Language
1.0	I-Language
documents	O
only	O
:	O
</s>
<s>
Include	O
both	O
xml:lang	B-Protocol
and	O
lang	O
attributes	O
on	O
any	O
elements	O
assigning	O
language	O
.	O
</s>
<s>
Use	O
the	O
empty-element	O
syntax	O
only	O
for	O
elements	O
specified	O
as	O
empty	O
in	O
HTML	B-Language
.	O
</s>
<s>
Include	O
an	O
extra	O
space	O
in	O
empty-element	O
tags	B-General_Concept
:	O
for	O
example	O
instead	O
of	O
.	O
</s>
<s>
Include	O
explicit	O
close	O
tags	B-General_Concept
for	O
elements	O
that	O
permit	O
content	O
but	O
are	O
left	O
empty	O
(	O
for	O
example	O
,	O
,	O
not	O
)	O
.	O
</s>
<s>
Omit	O
the	O
XML	B-Protocol
declaration	O
.	O
</s>
<s>
By	O
carefully	O
following	O
the	O
W3C	O
's	O
compatibility	O
guidelines	O
,	O
a	O
user	B-Protocol
agent	I-Protocol
should	O
be	O
able	O
to	O
interpret	O
the	O
document	O
equally	O
as	O
HTML	B-Language
or	O
XHTML	B-Language
.	O
</s>
<s>
For	O
documents	O
that	O
are	O
XHTML	B-Language
1.0	I-Language
and	O
have	O
been	O
made	O
compatible	O
in	O
this	O
way	O
,	O
the	O
W3C	O
permits	O
them	O
to	O
be	O
served	O
either	O
as	O
HTML	B-Language
(	O
with	O
a	O
text/html	B-Language
MIME	B-Application
type	I-Application
)	O
,	O
or	O
as	O
XHTML	B-Language
(	O
with	O
an	O
application/xhtml	O
+xml	O
or	O
application/xml	O
MIME	B-Application
type	I-Application
)	O
.	O
</s>
<s>
When	O
delivered	O
as	O
XHTML	B-Language
,	O
browsers	B-Application
should	O
use	O
an	O
XML	B-Protocol
parser	I-Protocol
,	O
which	O
adheres	O
strictly	O
to	O
the	O
XML	B-Protocol
specifications	I-Protocol
for	O
parsing	O
the	O
document	O
's	O
contents	O
.	O
</s>
<s>
HTML	B-Language
4	O
defined	O
three	O
different	O
versions	O
of	O
the	O
language	O
:	O
Strict	O
,	O
Transitional	O
(	O
once	O
called	O
Loose	O
)	O
,	O
and	O
Frameset	B-General_Concept
.	O
</s>
<s>
The	O
Strict	O
version	O
is	O
intended	O
for	O
new	O
documents	O
and	O
is	O
considered	O
best	O
practice	O
,	O
while	O
the	O
Transitional	O
and	O
Frameset	B-General_Concept
versions	O
were	O
developed	O
to	O
make	O
it	O
easier	O
to	O
transition	O
documents	O
that	O
conformed	O
to	O
older	O
HTML	B-Language
specifications	O
or	O
did	O
n't	O
conform	O
to	O
any	O
specification	O
to	O
a	O
version	O
of	O
HTML	B-Language
4	O
.	O
</s>
<s>
The	O
Transitional	O
and	O
Frameset	B-General_Concept
versions	O
allow	O
for	O
presentational	O
markup	O
,	O
which	O
is	O
omitted	O
in	O
the	O
Strict	O
version	O
.	O
</s>
<s>
Instead	O
,	O
cascading	B-Language
style	I-Language
sheets	I-Language
are	O
encouraged	O
to	O
improve	O
the	O
presentation	O
of	O
HTML	B-Language
documents	O
.	O
</s>
<s>
Because	O
XHTML	B-Language
1	O
only	O
defines	O
an	O
XML	B-Protocol
syntax	O
for	O
the	O
language	O
defined	O
by	O
HTML	B-Language
4	O
,	O
the	O
same	O
differences	O
apply	O
to	O
XHTML	B-Language
1	O
as	O
well	O
.	O
</s>
<s>
underline	O
(	O
u	O
)	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
center	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
use	O
CSS	B-Language
instead	O
.	O
)	O
</s>
<s>
font	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
use	O
CSS	B-Language
instead	O
.	O
)	O
</s>
<s>
basefont	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
use	O
CSS	B-Language
instead	O
.	O
)	O
</s>
<s>
background	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
use	O
CSS	B-Language
instead	O
.	O
)	O
</s>
<s>
and	O
bgcolor	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
use	O
CSS	B-Language
instead	O
.	O
)	O
</s>
<s>
align	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
use	O
CSS	B-Language
instead	O
.	O
)	O
</s>
<s>
align	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
use	O
CSS	B-Language
instead	O
.	O
</s>
<s>
)	O
,	O
noshade	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
use	O
CSS	B-Language
instead	O
.	O
</s>
<s>
)	O
,	O
size	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
use	O
CSS	B-Language
instead	O
.	O
)	O
</s>
<s>
and	O
width	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
use	O
CSS	B-Language
instead	O
.	O
)	O
</s>
<s>
align	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
use	O
CSS	B-Language
instead	O
.	O
</s>
<s>
align	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
use	O
CSS	B-Language
instead	O
.	O
)	O
</s>
<s>
align	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
use	O
CSS	B-Language
instead	O
.	O
)	O
</s>
<s>
and	O
bgcolor	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
use	O
CSS	B-Language
instead	O
.	O
)	O
</s>
<s>
nowrap	O
(	O
Obsolete	O
)	O
,	O
bgcolor	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
use	O
CSS	B-Language
instead	O
.	O
</s>
<s>
bgcolor	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
use	O
CSS	B-Language
instead	O
.	O
)	O
</s>
<s>
type	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
use	O
CSS	B-Language
instead	O
.	O
</s>
<s>
)	O
,	O
compact	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
use	O
CSS	B-Language
instead	O
.	O
)	O
</s>
<s>
and	O
start	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
use	O
CSS	B-Language
instead	O
.	O
)	O
</s>
<s>
menu	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
use	O
CSS	B-Language
instead	O
.	O
)	O
</s>
<s>
dir	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
use	O
CSS	B-Language
instead	O
.	O
)	O
</s>
<s>
isindex	O
(	O
Deprecated	B-General_Concept
.	O
)	O
</s>
<s>
applet	O
(	O
Deprecated	B-General_Concept
.	O
</s>
<s>
target	O
(	O
Deprecated	B-General_Concept
in	O
the	O
map	O
,	O
link	O
and	O
form	O
elements	O
.	O
)	O
</s>
<s>
The	O
Frameset	B-General_Concept
version	O
includes	O
everything	O
in	O
the	O
Transitional	O
version	O
,	O
as	O
well	O
as	O
the	O
frameset	B-General_Concept
element	O
(	O
used	O
instead	O
of	O
body	O
)	O
and	O
the	O
frame	B-General_Concept
element	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
above	O
transitional	O
differences	O
,	O
the	O
frameset	B-General_Concept
specifications	O
(	O
whether	O
XHTML	B-Language
1.0	I-Language
or	O
HTML	B-Language
4.01	I-Language
)	O
specify	O
a	O
different	O
content	O
model	O
,	O
with	O
frameset	B-General_Concept
replacing	O
body	O
,	O
that	O
contains	O
either	O
frame	B-General_Concept
elements	O
,	O
or	O
optionally	O
noframes	B-General_Concept
with	O
a	O
body	O
.	O
</s>
<s>
However	O
,	O
contrary	O
to	O
popular	O
misconceptions	O
,	O
the	O
move	O
to	O
XHTML	B-Language
does	O
not	O
imply	O
a	O
removal	O
of	O
this	O
legacy	O
support	O
.	O
</s>
<s>
Rather	O
the	O
X	O
in	O
XML	B-Protocol
stands	O
for	O
extensible	O
and	O
the	O
W3C	O
is	O
modularizing	O
the	O
entire	O
specification	O
and	O
opens	O
it	O
up	O
to	O
independent	O
extensions	O
.	O
</s>
<s>
The	O
primary	O
achievement	O
in	O
the	O
move	O
from	O
XHTML	B-Language
1.0	I-Language
to	O
XHTML	B-Language
1.1	O
is	O
the	O
modularization	O
of	O
the	O
entire	O
specification	O
.	O
</s>
<s>
The	O
strict	O
version	O
of	O
HTML	B-Language
is	O
deployed	O
in	O
XHTML	B-Language
1.1	O
through	O
a	O
set	O
of	O
modular	O
extensions	O
to	O
the	O
base	O
XHTML	B-Language
1.1	O
specification	O
.	O
</s>
<s>
Likewise	O
,	O
someone	O
looking	O
for	O
the	O
loose	O
(	O
transitional	O
)	O
or	O
frameset	B-General_Concept
specifications	O
will	O
find	O
similar	O
extended	O
XHTML	B-Language
1.1	O
support	O
(	O
much	O
of	O
it	O
is	O
contained	O
in	O
the	O
legacy	O
or	O
frame	B-General_Concept
modules	O
)	O
.	O
</s>
<s>
So	O
for	O
example	O
,	O
XHTML	B-Language
1.1	O
will	O
allow	O
quicker	O
migration	O
to	O
emerging	O
XML	B-Protocol
standards	O
such	O
as	O
MathML	B-Language
(	O
a	O
presentational	O
and	O
semantic	B-Application
math	O
language	O
based	O
on	O
XML	B-Protocol
)	O
and	O
XForms	B-Application
—	O
a	O
new	O
highly	O
advanced	O
web-form	O
technology	O
to	O
replace	O
the	O
existing	O
HTML	B-Language
forms	O
.	O
</s>
<s>
In	O
summary	O
,	O
the	O
HTML	B-Language
4	O
specification	O
primarily	O
reined	O
in	O
all	O
the	O
various	O
HTML	B-Language
implementations	O
into	O
a	O
single	O
clearly	O
written	O
specification	O
based	O
on	O
SGML	B-Language
.	O
</s>
<s>
XHTML	B-Language
1.0	I-Language
,	O
ported	O
this	O
specification	O
,	O
as	O
is	O
,	O
to	O
the	O
new	O
XML-defined	O
specification	O
.	O
</s>
<s>
Next	O
,	O
XHTML	B-Language
1.1	O
takes	O
advantage	O
of	O
the	O
extensible	O
nature	O
of	O
XML	B-Protocol
and	O
modularizes	O
the	O
whole	O
specification	O
.	O
</s>
<s>
XHTML	B-Language
2.0	O
was	O
intended	O
to	O
be	O
the	O
first	O
step	O
in	O
adding	O
new	O
features	O
to	O
the	O
specification	O
in	O
a	O
standards-body-based	O
approach	O
.	O
</s>
<s>
The	O
HTML	B-Language
Living	O
Standard	O
,	O
which	O
is	O
developed	O
by	O
WHATWG	B-Language
,	O
is	O
the	O
official	O
version	O
,	O
while	O
W3C	O
HTML5	B-Application
is	O
no	O
longer	O
separate	O
from	O
WHATWG	B-Language
.	O
</s>
<s>
There	O
are	O
some	O
WYSIWYG	B-Application
editors	I-Application
(	O
What	B-Application
You	I-Application
See	I-Application
Is	I-Application
What	I-Application
You	I-Application
Get	I-Application
)	O
,	O
in	O
which	O
the	O
user	O
lays	O
out	O
everything	O
as	O
it	O
is	O
to	O
appear	O
in	O
the	O
HTML	B-Language
document	O
using	O
a	O
graphical	B-Application
user	I-Application
interface	I-Application
(	O
GUI	B-Application
)	O
,	O
often	O
similar	O
to	O
word	B-General_Concept
processors	I-General_Concept
.	O
</s>
<s>
The	O
editor	O
renders	O
the	O
document	O
rather	O
than	O
showing	O
the	O
code	O
,	O
so	O
authors	O
do	O
not	O
require	O
extensive	O
knowledge	O
of	O
HTML	B-Language
.	O
</s>
<s>
The	O
WYSIWYG	B-Application
editing	O
model	O
has	O
been	O
criticized	O
,	O
primarily	O
because	O
of	O
the	O
low	O
quality	O
of	O
the	O
generated	O
code	O
;	O
there	O
are	O
voices	O
advocating	O
a	O
change	O
to	O
the	O
WYSIWYM	B-General_Concept
model	O
(	O
What	O
You	O
See	O
Is	O
What	O
You	O
Mean	O
)	O
.	O
</s>
<s>
WYSIWYG	B-Application
editors	I-Application
remain	O
a	O
controversial	O
topic	O
because	O
of	O
their	O
perceived	O
flaws	O
such	O
as	O
:	O
</s>
<s>
Often	O
producing	O
extremely	O
verbose	O
and	O
redundant	O
code	O
that	O
fails	O
to	O
make	O
use	O
of	O
the	O
cascading	O
nature	O
of	O
HTML	B-Language
and	O
CSS	B-Language
.	O
</s>
<s>
Often	O
producing	O
ungrammatical	O
markup	O
,	O
called	O
tag	B-General_Concept
soup	I-General_Concept
or	O
semantically	O
incorrect	O
markup	O
(	O
such	O
as	O
for	O
italics	O
)	O
.	O
</s>
<s>
As	O
a	O
great	O
deal	O
of	O
the	O
information	O
in	O
HTML	B-Language
documents	O
is	O
not	O
in	O
the	O
layout	O
,	O
the	O
model	O
has	O
been	O
criticized	O
for	O
its	O
"	O
what	O
you	O
see	O
is	O
all	O
you	O
get	O
"	O
-nature	O
.	O
</s>
