<s>
In	O
computing	O
,	O
version	B-Protocol
targeting	I-Protocol
is	O
a	O
technique	O
that	O
allows	O
a	O
group	O
of	O
(	O
presumably	O
knowledgeable	O
)	O
users	O
(	O
including	O
software	B-Application
developers	I-Application
)	O
to	O
use	O
some	O
advanced	O
software	O
features	O
that	O
were	O
introduced	O
in	O
a	O
particular	O
software	O
version	O
while	O
allowing	O
users	O
accustomed	O
to	O
the	O
prior	O
versions	O
to	O
still	O
use	O
the	O
same	O
software	O
as	O
if	O
the	O
new	O
features	O
were	O
never	O
added	O
to	O
the	O
software	O
.	O
</s>
<s>
It	O
is	O
a	O
way	O
to	O
ensure	O
backward	B-General_Concept
compatibility	I-General_Concept
when	O
new	O
software	O
features	O
would	O
otherwise	O
break	O
it	O
.	O
</s>
<s>
Version	B-Protocol
targeting	I-Protocol
has	O
been	O
used	O
in	O
Mozilla	B-Application
Firefox	I-Application
when	O
it	O
introduced	O
JavaScript	B-Language
1.6	I-Language
in	O
Firefox	B-Application
1.5	O
and	O
JavaScript	B-Language
1.7	I-Language
in	O
Firefox	B-Language
2.0	I-Language
:	O
developers	B-Application
willing	O
to	O
use	O
the	O
new	O
scripting	B-Language
engine	I-Language
had	O
to	O
explicitly	O
opt-in	O
.	O
</s>
<s>
Version	B-Protocol
targeting	I-Protocol
was	O
proposed	O
by	O
Microsoft	O
for	O
use	O
in	O
its	O
Internet	B-Application
Explorer	I-Application
8	I-Application
product-in-development	O
,	O
but	O
the	O
idea	O
was	O
later	O
discarded	O
.	O
</s>
<s>
The	O
proposal	O
came	O
after	O
the	O
release	O
of	O
Internet	B-Application
Explorer	I-Application
7	I-Application
which	O
improved	O
its	O
CSS	B-Language
2.1	I-Language
support	O
at	O
the	O
cost	O
of	O
causing	O
some	O
websites	O
that	O
were	O
developed	O
for	O
Internet	B-Application
Explorer	I-Application
6	I-Application
to	O
be	O
rendered	O
incorrectly	O
when	O
viewed	O
with	O
the	O
new	O
browser	O
version	O
.	O
</s>
<s>
Microsoft	O
contacted	O
the	O
Web	O
Standards	O
Project	O
and	O
experts	O
on	O
Web	O
standards	O
and	O
asked	O
for	O
assistance	O
in	O
devising	O
a	O
new	O
DOCTYPE-like	O
technique	O
that	O
could	O
work	O
across	O
browsers	O
and	O
let	O
Web	B-Operating_System
developers	I-Operating_System
specify	O
exact	O
browser	O
versions	O
under	O
which	O
their	O
Web	O
sites	O
are	O
known	O
to	O
work	O
correctly	O
,	O
and	O
browsers	O
implementing	O
this	O
form	O
of	O
version	B-Protocol
targeting	I-Protocol
would	O
use	O
the	O
correct	O
rendering	O
engine	O
versions	O
to	O
display	O
the	O
site	O
correctly	O
.	O
</s>
<s>
Members	O
of	O
the	O
WaSP	B-Application
Microsoft	O
Task	O
Force	O
were	O
involved	O
in	O
the	O
proposal	O
,	O
albeit	O
not	O
every	O
member	O
backed	O
it	O
.	O
</s>
<s>
Some	O
commentators	O
suggested	O
that	O
it	O
would	O
be	O
possible	O
to	O
use	O
Internet	B-Application
Explorer	I-Application
8	I-Application
's	O
support	O
for	O
new	O
DOCTYPEs	O
in	O
order	O
to	O
avoid	O
using	O
its	O
version	B-Protocol
targeting	I-Protocol
meta	O
tag	O
.	O
</s>
<s>
The	O
concept	O
of	O
version	B-Protocol
targeting	I-Protocol
,	O
especially	O
as	O
proposed	O
by	O
Microsoft	O
,	O
has	O
been	O
criticised	O
for	O
being	O
a	O
new	O
form	O
of	O
browser	B-Protocol
sniffing	I-Protocol
and	O
for	O
violating	O
the	O
principle	O
of	O
forward-compatible	B-General_Concept
development	O
where	O
progressive	O
enhancement	O
is	O
preferred	O
.	O
</s>
<s>
Version	B-Protocol
targeting	I-Protocol
has	O
been	O
criticised	O
for	O
not	O
giving	O
incentives	O
to	O
developers	B-Application
to	O
plan	O
ahead	O
for	O
forward	B-General_Concept
compatibility	I-General_Concept
.	O
</s>
<s>
Version	B-Protocol
targeting	I-Protocol
has	O
been	O
welcomed	O
by	O
some	O
people	O
as	O
a	O
means	O
to	O
enable	O
browsers	O
to	O
adopt	O
Web	O
standards	O
without	O
breaking	O
compatibility	O
with	O
Web	O
sites	O
depended	O
on	O
old	O
rendering	O
engines	O
for	O
their	O
functionality	O
.	O
</s>
