<s>
The	O
data	B-Protocol
URI	I-Protocol
scheme	I-Protocol
is	O
a	O
uniform	B-Protocol
resource	I-Protocol
identifier	I-Protocol
(	O
URI	B-Protocol
)	O
scheme	O
that	O
provides	O
a	O
way	O
to	O
include	O
data	O
in-line	O
in	O
Web	O
pages	O
as	O
if	O
they	O
were	O
external	O
resources	O
.	O
</s>
<s>
This	O
technique	O
allows	O
normally	O
separate	O
elements	O
such	O
as	O
images	O
and	O
style	O
sheets	O
to	O
be	O
fetched	O
in	O
a	O
single	O
Hypertext	B-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
(	O
HTTP	B-Protocol
)	O
request	O
,	O
which	O
may	O
be	O
more	O
efficient	O
than	O
multiple	O
HTTP	B-Protocol
requests	I-Protocol
,	O
and	O
used	O
by	O
several	O
browser	O
extensions	O
to	O
package	O
images	O
as	O
well	O
as	O
other	O
multimedia	O
contents	O
in	O
a	O
single	O
HTML	B-Language
file	I-Language
for	O
page	O
saving	O
.	O
</s>
<s>
,	O
data	B-Protocol
URIs	I-Protocol
are	O
fully	O
supported	O
by	O
most	O
major	O
browsers	O
,	O
and	O
partially	O
supported	O
in	O
Internet	B-Application
Explorer	I-Application
.	O
</s>
<s>
The	O
syntax	O
of	O
data	B-Protocol
URIs	I-Protocol
is	O
defined	O
in	O
Request	O
for	O
Comments	O
(	O
RFC	O
)	O
2397	O
,	O
published	O
in	O
August	O
1998	O
,	O
and	O
follows	O
the	O
URI	B-Protocol
scheme	O
syntax	O
.	O
</s>
<s>
A	O
data	B-Protocol
URI	I-Protocol
consists	O
of	O
:	O
</s>
<s>
An	O
optional	O
media	B-Application
type	I-Application
.	O
</s>
<s>
The	O
media	B-Application
type	I-Application
part	O
may	O
include	O
one	O
or	O
more	O
parameters	O
,	O
in	O
the	O
format	O
attribute	O
=	O
value	O
,	O
separated	O
by	O
semicolons	O
(	O
;	O
)	O
.	O
</s>
<s>
A	O
common	O
media	B-Application
type	I-Application
parameter	O
is	O
charset	B-General_Concept
,	O
specifying	O
the	O
character	B-General_Concept
set	I-General_Concept
of	O
the	O
media	B-Application
type	I-Application
,	O
where	O
the	O
value	O
is	O
from	O
the	O
IANA	O
list	O
of	O
character	B-General_Concept
set	I-General_Concept
names	O
.	O
</s>
<s>
If	O
one	O
is	O
not	O
specified	O
,	O
the	O
media	B-Application
type	I-Application
of	O
the	O
data	B-Protocol
URI	I-Protocol
is	O
assumed	O
to	O
be	O
text/plain	O
;	O
charset	B-General_Concept
=	O
US-ASCII	O
.	O
</s>
<s>
An	O
optional	O
base64	B-Protocol
extension	O
base64	B-Protocol
,	O
separated	O
from	O
the	O
preceding	O
part	O
by	O
a	O
semicolon	O
.	O
</s>
<s>
When	O
present	O
,	O
this	O
indicates	O
that	O
the	O
data	O
content	O
of	O
the	O
URI	B-Protocol
is	O
binary	O
data	O
,	O
encoded	O
in	O
ASCII	O
format	O
using	O
the	O
Base64	B-Protocol
scheme	O
for	O
binary-to-text	O
encoding	O
.	O
</s>
<s>
The	O
base64	B-Protocol
extension	O
is	O
distinguished	O
from	O
any	O
media	B-Application
type	I-Application
parameters	O
by	O
virtue	O
of	O
not	O
having	O
a	O
=	O
value	O
component	O
and	O
by	O
coming	O
after	O
any	O
media	B-Application
type	I-Application
parameters	O
.	O
</s>
<s>
Since	O
Base64	B-Protocol
encoded	O
data	O
is	O
approximately	O
33%	O
larger	O
than	O
original	O
data	O
,	O
it	O
is	O
recommended	O
to	O
use	O
Base64	B-Protocol
data	B-Protocol
URIs	I-Protocol
only	O
if	O
the	O
server	O
supports	O
HTTP	B-Protocol
compression	I-Protocol
or	O
embedded	O
files	O
are	O
smaller	O
than	O
1KB	O
.	O
</s>
<s>
The	O
comma	O
is	O
required	O
in	O
a	O
data	B-Protocol
URI	I-Protocol
,	O
even	O
when	O
the	O
data	O
part	O
has	O
zero	O
length	O
.	O
</s>
<s>
Note	O
that	O
this	O
may	O
include	O
characters	O
,	O
such	O
as	O
colon	O
,	O
semicolon	O
,	O
and	O
comma	O
which	O
are	O
delimiters	O
in	O
the	O
URI	B-Protocol
components	O
preceding	O
the	O
data	O
part	O
.	O
</s>
<s>
If	O
the	O
data	O
is	O
Base64-encoded	O
,	O
then	O
the	O
data	O
part	O
may	O
contain	O
only	O
valid	O
Base64	B-Protocol
characters	O
.	O
</s>
<s>
Note	O
that	O
Base64-encoded	O
data	B-Protocol
:	I-Protocol
URIs	I-Protocol
use	O
the	O
standard	O
Base64	B-Protocol
character	B-General_Concept
set	I-General_Concept
(	O
with	O
'	O
+	O
 '	O
and	O
'	O
/	O
'	O
as	O
characters	O
62	O
and	O
63	O
)	O
rather	O
than	O
the	O
so-called	O
"	O
URL-safe	O
Base64	B-Protocol
"	O
character	B-General_Concept
set	I-General_Concept
.	O
</s>
<s>
Examples	O
of	O
data	B-Protocol
URIs	I-Protocol
showing	O
most	O
of	O
the	O
features	O
are	O
:	O
</s>
<s>
Thus	O
,	O
within	O
the	O
overall	O
URI	B-Protocol
syntax	O
,	O
a	O
data	B-Protocol
URI	I-Protocol
consists	O
of	O
a	O
scheme	O
and	O
a	O
path	O
,	O
with	O
no	O
authority	O
part	O
,	O
query	O
string	O
,	O
or	O
fragment	O
.	O
</s>
<s>
URI	B-Protocol
path	O
.	O
</s>
<s>
An	O
HTML	B-Language
fragment	O
embedding	O
a	O
picture	O
of	O
a	O
small	O
red	O
dot	O
:	O
</s>
<s>
In	O
actual	O
URIs	B-Protocol
,	O
</s>
<s>
including	O
data	B-Protocol
URIs	I-Protocol
,	O
control	O
characters	O
(	O
ASCII	O
0	O
to	O
31	O
,	O
and	O
127	O
)	O
and	O
spaces	O
(	O
ASCII	O
32	O
)	O
are	O
"	O
excluded	O
characters	O
"	O
.	O
</s>
<s>
This	O
means	O
that	O
whitespace	O
characters	O
are	O
not	O
permitted	O
in	O
data	B-Protocol
URIs	I-Protocol
.	O
</s>
<s>
However	O
,	O
in	O
the	O
context	O
of	O
HTML	B-Language
4	O
and	O
HTML	B-Language
5	O
,	O
linefeeds	O
within	O
an	O
element	O
attribute	O
value	O
(	O
such	O
as	O
the	O
"	O
src	O
"	O
above	O
)	O
are	O
ignored	O
.	O
</s>
<s>
So	O
the	O
data	B-Protocol
URI	I-Protocol
above	O
would	O
be	O
processed	O
ignoring	O
the	O
linefeeds	O
,	O
giving	O
the	O
correct	O
result	O
.	O
</s>
<s>
But	O
note	O
that	O
this	O
is	O
an	O
HTML	B-Language
feature	O
,	O
not	O
a	O
data	B-Protocol
URI	I-Protocol
feature	O
,	O
and	O
in	O
other	O
contexts	O
,	O
it	O
is	O
not	O
possible	O
to	O
rely	O
on	O
whitespace	O
within	O
the	O
URI	B-Protocol
being	O
ignored	O
.	O
</s>
<s>
A	O
Cascading	B-Language
Style	I-Language
Sheets	I-Language
(	O
CSS	B-Language
)	O
rule	O
that	O
includes	O
a	O
background	O
image	O
:	O
</s>
<s>
are	O
a	O
feature	O
of	O
CSS	B-Language
,	O
indicating	O
continuation	O
on	O
the	O
next	O
line	O
.	O
</s>
<s>
These	O
would	O
be	O
removed	O
by	O
the	O
CSS	B-Language
stylesheet	I-Language
processor	O
,	O
and	O
the	O
data	B-Protocol
URI	I-Protocol
would	O
be	O
reconstituted	O
without	O
whitespace	O
,	O
making	O
it	O
correct	O
,	O
since	O
whitespace	O
is	O
not	O
allowed	O
within	O
the	O
data	O
component	O
of	O
a	O
data	B-Protocol
:	I-Protocol
</s>
<s>
URI	B-Protocol
.	O
</s>
<s>
A	O
JavaScript	B-Language
statement	O
that	O
opens	O
an	O
embedded	O
subwindow	O
,	O
as	O
for	O
a	O
footnote	O
link	O
:	O
</s>
<s>
A	O
Scalable	B-Application
Vector	I-Application
Graphic	I-Application
image	O
containing	O
an	O
embedded	O
JPEG	O
image	O
encoded	O
in	O
Base64	B-Protocol
:	O
</s>
<s>
The	O
data	B-Protocol
URI	I-Protocol
can	O
be	O
utilized	O
to	O
construct	O
attack	O
pages	O
that	O
attempt	O
to	O
obtain	O
usernames	O
and	O
passwords	O
from	O
unsuspecting	O
web	O
users	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
some	O
browsers	O
now	O
block	O
webpages	O
from	O
navigating	O
to	O
data	B-Protocol
URIs	I-Protocol
.	O
</s>
