<s>
A	O
canonical	B-General_Concept
link	I-General_Concept
element	I-General_Concept
is	O
an	O
HTML	B-General_Concept
element	I-General_Concept
that	O
helps	O
webmasters	O
prevent	O
duplicate	O
content	O
issues	O
in	O
search	B-Application
engine	I-Application
optimization	O
by	O
specifying	O
the	O
"	O
canonical	B-General_Concept
"	O
or	O
"	O
preferred	O
"	O
version	O
of	O
a	O
web	O
page	O
.	O
</s>
<s>
A	O
major	O
problem	O
for	O
search	B-Application
engines	I-Application
is	O
to	O
determine	O
the	O
original	O
source	O
for	O
documents	O
that	O
are	O
available	O
on	O
multiple	O
URLs	O
.	O
</s>
<s>
For	O
example	O
,	O
would	O
be	O
considered	O
by	O
search	B-Application
engines	I-Application
to	O
be	O
an	O
entirely	O
different	O
page	O
from	O
,	O
even	O
though	O
both	O
URLs	O
may	O
reference	O
the	O
same	O
content	O
.	O
</s>
<s>
In	O
February	O
2009	O
,	O
Google	B-Application
,	O
Yahoo	B-Application
and	O
Microsoft	O
announced	O
support	O
for	O
the	O
canonical	B-General_Concept
link	I-General_Concept
element	I-General_Concept
,	O
which	O
can	O
be	O
inserted	O
into	O
the	O
section	O
of	O
a	O
web	O
page	O
,	O
to	O
allow	O
webmasters	O
to	O
prevent	O
these	O
issues	O
.	O
</s>
<s>
The	O
canonical	B-General_Concept
link	I-General_Concept
element	I-General_Concept
helps	O
webmasters	O
make	O
clear	O
to	O
the	O
search	B-Application
engines	I-Application
which	O
page	O
should	O
be	O
credited	O
as	O
the	O
original	O
.	O
</s>
<s>
Search	B-Application
engines	I-Application
try	O
to	O
utilize	O
canonical	B-General_Concept
link	O
definitions	O
as	O
an	O
output	O
filter	O
for	O
their	O
search	B-Application
results	I-Application
.	O
</s>
<s>
If	O
multiple	O
URLs	O
contain	O
the	O
same	O
content	O
in	O
the	O
result	O
set	O
,	O
the	O
canonical	B-General_Concept
link	O
URL	O
definitions	O
will	O
likely	O
be	O
incorporated	O
to	O
determine	O
the	O
original	O
source	O
of	O
the	O
content	O
.	O
</s>
<s>
"	O
For	O
example	O
,	O
when	O
Google	B-Application
finds	O
identical	O
content	O
instances	O
,	O
it	O
decides	O
to	O
show	O
one	O
of	O
them	O
.	O
</s>
<s>
Its	O
choice	O
of	O
the	O
resource	O
to	O
display	O
in	O
the	O
search	B-Application
results	I-Application
will	O
depend	O
upon	O
the	O
search	O
query.	O
"	O
</s>
<s>
According	O
to	O
Google	B-Application
,	O
the	O
canonical	B-General_Concept
link	I-General_Concept
element	I-General_Concept
is	O
not	O
considered	O
to	O
be	O
a	O
directive	O
,	O
but	O
rather	O
a	O
hint	O
that	O
the	O
ranking	O
algorithm	O
will	O
"	O
honor	O
strongly.	O
"	O
</s>
<s>
While	O
the	O
canonical	B-General_Concept
link	I-General_Concept
element	I-General_Concept
has	O
its	O
benefits	O
,	O
Matt	O
Cutts	O
,	O
then	O
the	O
head	O
of	O
Google	B-Application
's	I-Application
webspam	O
team	O
,	O
has	O
said	O
that	O
the	O
search	B-Application
engine	I-Application
prefers	O
the	O
use	O
of	O
301	O
redirects	O
.	O
</s>
<s>
Cutts	O
said	O
the	O
preference	O
for	O
redirects	O
is	O
because	O
Google	B-Application
's	I-Application
spiders	B-Application
can	O
choose	O
to	O
ignore	O
a	O
canonical	B-General_Concept
link	I-General_Concept
element	I-General_Concept
if	O
they	O
deem	O
it	O
more	O
beneficial	O
to	O
do	O
so	O
.	O
</s>
<s>
The	O
canonical	B-General_Concept
link	I-General_Concept
element	I-General_Concept
can	O
be	O
either	O
used	O
in	O
the	O
semantic	B-Application
HTML	O
or	O
sent	O
with	O
the	O
HTTP	B-Protocol
header	I-Protocol
of	O
a	O
document	O
.	O
</s>
<s>
For	O
non	O
HTML	O
documents	O
,	O
the	O
HTTP	B-Protocol
header	I-Protocol
is	O
an	O
alternate	O
way	O
to	O
set	O
a	O
canonical	B-General_Concept
URL	O
.	O
</s>
<s>
By	O
the	O
HTML	O
5	O
standard	O
,	O
the	O
HTML	B-General_Concept
element	I-General_Concept
must	O
be	O
within	O
the	O
section	O
of	O
the	O
document	O
.	O
</s>
<s>
Some	O
sites	O
such	O
as	O
Stack	B-Error_Name
Overflow	I-Error_Name
have	O
on-page	O
hyperlinks	O
which	O
link	O
to	O
a	O
clean	B-Protocol
URL	I-Protocol
of	O
themselves	O
.	O
</s>
<s>
Usability	B-General_Concept
benefits	O
are	O
facilitating	O
copying	O
the	O
hyperlink	O
target	O
URL	O
or	O
title	O
if	O
the	O
browser	O
or	O
a	O
browser	B-Protocol
extension	I-Protocol
offers	O
a	O
"	O
Copy	O
link	O
text	O
"	O
context	O
menu	O
option	O
for	O
hyperlinks	O
,	O
the	O
ability	O
for	O
the	O
original	O
URL	O
to	O
be	O
retrieved	O
from	O
a	O
saved	O
page	O
if	O
not	O
stored	O
by	O
the	O
browser	O
into	O
a	O
comment	O
inside	O
the	O
file	O
,	O
as	O
well	O
as	O
the	O
ability	O
to	O
duplicate	O
the	O
opened	O
page	O
into	O
a	O
new	O
tab	O
right	O
next	O
to	O
the	O
currently	O
opened	O
one	O
if	O
the	O
browser	O
lacks	O
such	O
a	O
feature	O
.	O
</s>
<s>
Below	O
is	O
an	O
example	O
of	O
HTML	O
code	O
that	O
uses	O
the	O
inside	O
the	O
tag	B-General_Concept
.	O
</s>
<s>
The	O
code	O
could	O
be	O
used	O
on	O
a	O
page	O
such	O
as	O
to	O
tell	O
search	B-Application
engines	I-Application
that	O
the	O
is	O
the	O
preferred	O
version	O
of	O
the	O
webpage	O
.	O
</s>
