<s>
Semantic	B-General_Concept
HTML	I-General_Concept
is	O
the	O
use	O
of	O
HTML	B-General_Concept
markup	I-General_Concept
to	O
reinforce	O
the	O
semantics	B-Application
,	O
or	O
meaning	O
,	O
of	O
the	O
information	O
in	O
web	O
pages	O
and	O
web	B-Application
applications	I-Application
rather	O
than	O
merely	O
to	O
define	O
its	O
presentation	O
or	O
look	O
.	O
</s>
<s>
Semantic	B-General_Concept
HTML	I-General_Concept
is	O
processed	O
by	O
traditional	O
web	B-Application
browsers	I-Application
as	O
well	O
as	O
by	O
many	O
other	O
user	B-Protocol
agents	I-Protocol
.	O
</s>
<s>
CSS	B-Language
is	O
used	O
to	O
suggest	O
its	O
presentation	O
to	O
human	O
users	O
.	O
</s>
<s>
HTML	B-Language
has	O
included	O
semantic	B-General_Concept
markup	I-General_Concept
since	O
its	O
inception	O
.	O
</s>
<s>
In	O
an	O
HTML	B-Language
document	O
,	O
the	O
author	O
may	O
,	O
among	O
other	O
things	O
,	O
"	O
start	O
with	O
a	O
title	O
;	O
add	O
headings	O
and	O
paragraphs	O
;	O
add	O
emphasis	O
to	O
 [ the ] 	O
text	O
;	O
add	O
images	O
;	O
add	O
links	O
to	O
other	O
pages	O
;	O
 [ and ] 	O
use	O
various	O
kinds	O
of	O
lists	O
"	O
.	O
</s>
<s>
Various	O
versions	O
of	O
the	O
HTML	B-Language
standard	O
have	O
included	O
presentational	O
markup	O
such	O
as	O
<font> (added in HTML 3.2; removed in HTML 4.0 Strict ) , <i> (all versions )  and <center>	O
(	O
added	O
in	O
HTML	B-Language
3.2	O
)	O
.	O
</s>
<s>
There	O
are	O
also	O
the	O
semantically	O
neutral	O
span	B-General_Concept
and	I-General_Concept
div	I-General_Concept
elements	I-General_Concept
.	O
</s>
<s>
Since	O
the	O
late	O
1990s	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>
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	B-Application
application	I-Application
hybrids	O
and	O
Berners-Lee	O
'	O
s	O
semantic	O
agents	O
lies	O
in	O
the	O
fact	O
that	O
the	O
current	O
aggregation	B-Application
and	O
hybridisation	O
of	O
information	O
is	O
usually	O
designed	O
in	O
by	O
web	O
developers	O
,	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	O
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
.	O
</s>
<s>
In	O
order	O
for	O
search-engine	B-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
,	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	O
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
published	O
information	O
.	O
</s>
<s>
While	O
the	O
true	O
semantic	O
web	O
may	O
depend	O
on	O
complex	O
RDF	O
ontologies	O
and	O
metadata	O
,	O
every	O
HTML	B-Language
document	O
makes	O
its	O
contribution	O
to	O
the	O
meaningfulness	O
of	O
the	O
Web	O
by	O
the	O
correct	O
use	O
of	O
headings	O
,	O
lists	O
,	O
titles	O
and	O
other	O
semantic	B-General_Concept
markup	I-General_Concept
wherever	O
possible	O
.	O
</s>
<s>
This	O
"	O
plain	O
"	O
use	O
of	O
HTML	B-Language
has	O
been	O
called	O
"	O
Plain	O
Old	O
Semantic	B-General_Concept
HTML	I-General_Concept
"	O
or	O
POSH	O
.	O
</s>
<s>
The	O
correct	O
use	O
of	O
Web	O
2.0	O
'	O
tagging	O
 '	O
creates	O
folksonomies	B-General_Concept
that	O
may	O
be	O
equally	O
or	O
even	O
more	O
meaningful	O
to	O
many	O
.	O
</s>
<s>
HTML	B-Application
5	I-Application
introduced	O
new	O
semantic	O
elements	O
such	O
as	O
section	O
,	O
article	O
,	O
footer	O
,	O
progress	O
,	O
nav	O
,	O
aside	O
,	O
mark	O
,	O
and	O
time	O
.	O
</s>
<s>
Overall	O
,	O
the	O
goal	O
of	O
the	O
W3C	O
is	O
to	O
slowly	O
introduce	O
more	O
ways	O
for	O
browsers	B-Application
,	O
developers	O
,	O
and	O
crawlers	O
to	O
better	O
distinguish	O
between	O
different	O
types	O
of	O
data	O
,	O
allowing	O
for	O
benefits	O
such	O
as	O
better	O
display	O
on	O
browsers	B-Application
on	O
different	O
devices	O
.	O
</s>
<s>
Presentational	O
elements	O
were	O
not	O
formally	O
deprecated	B-General_Concept
in	O
HTML	B-Language
4.01	I-Language
and	O
XHTML	O
recommendations	O
,	O
but	O
were	O
recommended	O
against	O
.	O
</s>
<s>
In	O
HTML	B-Application
5	I-Application
,	O
some	O
of	O
those	O
elements	O
,	O
such	O
as	O
i	O
and	O
b	O
,	O
are	O
still	O
specified	O
as	O
their	O
meaning	O
has	O
been	O
clearly	O
defined	O
"	O
as	O
to	O
be	O
stylistically	O
offset	O
from	O
the	O
normal	O
prose	O
without	O
conveying	O
any	O
extra	O
importance	O
"	O
.	O
</s>
<s>
In	O
cases	O
where	O
a	O
document	O
requires	O
more	O
precise	O
semantics	B-Application
than	O
those	O
expressed	O
in	O
HTML	B-Language
alone	O
,	O
fragments	O
of	O
the	O
document	O
may	O
be	O
enclosed	O
within	O
span	O
or	O
div	B-General_Concept
elements	I-General_Concept
with	O
meaningful	O
class	O
names	O
such	O
as	O
<span class="author"> and <div class="invoice">	O
.	O
</s>
<s>
Microformats	B-General_Concept
formalise	O
this	O
approach	O
to	O
semantics	B-Application
in	O
HTML	B-Language
.	O
</s>
<s>
A	O
means	O
of	O
marking-up	O
any	O
arbitrary	O
section	O
of	O
HTML	B-Language
would	O
require	O
a	O
mechanism	O
independent	O
of	O
the	O
markup	O
structure	O
itself	O
,	O
such	O
as	O
XPointer	B-General_Concept
.	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>
In	O
2010	O
,	O
Google	B-Application
specified	O
three	O
forms	O
of	O
structured	O
metadata	O
that	O
their	O
systems	O
will	O
use	O
to	O
find	O
structured	O
semantic	O
content	O
within	O
webpages	O
.	O
</s>
<s>
Such	O
information	O
,	O
when	O
related	O
to	O
reviews	O
,	O
people	O
profiles	O
,	O
business	O
listings	O
,	O
and	O
events	O
will	O
be	O
used	O
by	O
Google	B-Application
to	O
enhance	O
the	O
"	O
snippet	O
"	O
,	O
or	O
short	O
piece	O
of	O
quoted	O
text	O
that	O
is	O
shown	O
when	O
the	O
page	O
appears	O
in	O
search	O
listings	O
.	O
</s>
<s>
Google	B-Application
specifies	O
that	O
that	O
data	O
may	O
be	O
given	O
using	O
microdata	B-General_Concept
,	O
microformats	B-General_Concept
or	O
RDFa	B-General_Concept
.	O
</s>
<s>
Microdata	B-General_Concept
is	O
specified	O
inside	O
itemtype	O
and	O
itemprop	O
attributes	O
added	O
to	O
existing	O
HTML	B-General_Concept
elements	I-General_Concept
;	O
microformat	B-General_Concept
keywords	O
are	O
added	O
inside	O
class	O
attributes	O
as	O
discussed	O
above	O
;	O
and	O
RDFa	B-General_Concept
relies	O
on	O
rel	O
,	O
typeof	O
and	O
property	O
attributes	O
added	O
to	O
existing	O
elements	O
.	O
</s>
