<s>
A	O
browser	B-Protocol
engine	I-Protocol
(	O
also	O
known	O
as	O
a	O
layout	B-Protocol
engine	I-Protocol
or	O
rendering	O
engine	B-Application
)	O
is	O
a	O
core	O
software	O
component	O
of	O
every	O
major	O
web	B-Application
browser	I-Application
.	O
</s>
<s>
The	O
primary	O
job	O
of	O
a	O
browser	B-Protocol
engine	I-Protocol
is	O
to	O
transform	O
HTML	B-Language
documents	O
and	O
other	O
resources	O
of	O
a	O
web	O
page	O
into	O
an	O
interactive	O
visual	O
representation	O
on	O
a	O
user	O
's	O
device	O
.	O
</s>
<s>
A	O
browser	B-Protocol
engine	I-Protocol
is	O
not	O
a	O
stand-alone	O
computer	B-Application
program	I-Application
but	O
a	O
critical	O
piece	O
of	O
a	O
more	O
extensive	O
program	O
,	O
such	O
as	O
a	O
web	B-Application
browser	I-Application
,	O
from	O
which	O
the	O
term	O
is	O
derived	O
.	O
</s>
<s>
The	O
word	O
"	O
engine	B-Application
"	O
is	O
an	O
analogy	O
to	O
the	O
engine	B-Application
of	O
a	O
car	O
.	O
</s>
<s>
Besides	O
"	O
browser	B-Protocol
engine	I-Protocol
"	O
,	O
two	O
other	O
terms	O
are	O
in	O
everyday	O
use	O
regarding	O
related	O
concepts	O
:	O
"	O
layout	B-Protocol
engine	I-Protocol
"	O
and	O
"	O
rendering	O
engine	B-Application
"	O
.	O
</s>
<s>
In	O
practice	O
,	O
however	O
,	O
they	O
are	O
tightly	O
coupled	B-Application
and	O
rarely	O
considered	O
separately	O
.	O
</s>
<s>
In	O
addition	O
to	O
layout	O
and	O
rendering	O
,	O
a	O
browser	B-Protocol
engine	I-Protocol
enforces	O
the	O
security	B-Protocol
policy	I-Protocol
between	O
documents	O
,	O
handles	O
navigation	O
through	O
hyperlinks	O
and	O
data	O
submitted	O
through	O
forms	O
,	O
and	O
implements	O
the	O
Document	B-General_Concept
Object	I-General_Concept
Model	I-General_Concept
(	O
DOM	B-General_Concept
)	O
data	B-General_Concept
structure	I-General_Concept
exposed	O
to	O
page	O
scripts	B-Language
.	O
</s>
<s>
Executing	O
JavaScript	B-Language
(	O
JS	O
)	O
code	O
is	O
a	O
separate	O
matter	O
,	O
however	O
,	O
as	O
every	O
significant	O
web	B-Application
browser	I-Application
uses	O
a	O
dedicated	B-Language
engine	I-Language
for	O
this	O
.	O
</s>
<s>
The	O
JS	O
language	O
was	O
initially	O
created	O
for	O
use	O
in	O
browsers	B-Application
,	O
but	O
it	O
is	O
now	O
used	O
elsewhere	O
,	O
too	O
,	O
so	O
the	O
implementation	O
of	O
JS	B-Language
engines	I-Language
is	O
decoupled	O
from	O
browser	B-Protocol
engines	I-Protocol
.	O
</s>
<s>
The	O
two	O
engines	O
work	O
in	O
concert	O
via	O
the	O
shared	O
DOM	B-General_Concept
data	B-General_Concept
structure	I-General_Concept
in	O
a	O
web	B-Application
browser	I-Application
.	O
</s>
<s>
Browser	B-Protocol
engines	I-Protocol
are	O
used	O
in	O
other	O
types	O
of	O
programs	O
besides	O
web	B-Application
browsers	I-Application
.	O
</s>
<s>
Email	B-Protocol
clients	I-Protocol
need	O
them	O
to	O
display	O
HTML	B-Language
email	O
.	O
</s>
<s>
The	O
Electron	B-Operating_System
framework	I-Operating_System
,	O
which	O
is	O
powered	O
by	O
the	O
two	O
engines	O
of	O
the	B-Application
Google	I-Application
Chromium	B-Language
browser	I-Language
,	O
has	O
been	O
used	O
to	O
create	O
many	O
applications	B-Application
.	O
</s>
<s>
The	O
layout	O
of	O
a	O
web	O
page	O
is	O
typically	O
specified	O
by	O
Cascading	B-Language
Style	I-Language
Sheets	I-Language
(	O
CSS	B-Language
)	O
.	O
</s>
<s>
Each	O
style	O
sheet	O
is	O
a	O
series	O
of	O
rules	O
which	O
the	O
browser	B-Protocol
engine	I-Protocol
interprets	O
.	O
</s>
<s>
The	O
engine	B-Application
combines	O
all	O
relevant	O
CSS	B-Language
rules	O
to	O
calculate	O
precise	O
graphical	O
coordinates	O
for	O
the	O
visual	O
representation	O
it	O
will	O
paint	O
on	O
the	O
screen	O
.	O
</s>
<s>
Apple	O
created	O
the	O
WebKit	B-Language
engine	B-Application
for	O
its	O
Safari	B-Application
browser	I-Application
by	O
forking	B-Application
the	O
KHTML	B-Language
engine	B-Application
of	O
the	O
KDE	B-Application
project	O
.	O
</s>
<s>
All	O
browsers	B-Application
for	O
iOS	B-Application
must	O
use	O
WebKit	B-Language
as	O
their	O
engine	B-Application
.	O
</s>
<s>
Google	B-Application
originally	O
used	O
WebKit	B-Language
for	O
its	O
Chrome	B-Application
browser	I-Application
but	O
eventually	O
forked	O
it	O
to	O
create	O
the	O
Blink	B-Language
engine	B-Application
.	O
</s>
<s>
All	O
Chromium-based	O
browsers	B-Application
use	O
Blink	B-Language
,	O
as	O
do	O
applications	B-Application
built	O
with	O
CEF	B-Language
,	O
Electron	B-Operating_System
,	O
or	O
any	O
other	O
framework	B-Architecture
that	O
embeds	O
Chromium	B-Language
.	O
</s>
<s>
Microsoft	O
has	O
two	O
proprietary	B-Application
engines	O
,	O
Trident	B-Application
and	O
EdgeHTML	B-Application
.	O
</s>
<s>
Trident	B-Application
is	O
used	O
in	O
the	O
Internet	B-Application
Explorer	I-Application
browser	B-Application
.	O
</s>
<s>
EdgeHTML	B-Application
was	O
the	O
original	O
engine	B-Application
of	O
the	O
Edge	B-Application
browser	I-Application
,	O
but	O
that	O
was	O
remade	O
with	O
the	O
Blink	B-Language
engine	B-Application
.	O
</s>
<s>
EdgeHTML	B-Application
is	O
still	O
used	O
in	O
some	O
UWP	O
apps	O
.	O
</s>
<s>
Mozilla	B-Operating_System
develops	O
the	O
Gecko	B-Language
engine	I-Language
for	O
its	O
Firefox	B-Application
browser	I-Application
and	O
the	O
Thunderbird	B-Application
email	B-Protocol
client	I-Protocol
.	O
</s>
<s>
Only	O
the	O
duration	O
of	O
active	O
development	O
is	O
shown	O
,	O
which	O
is	O
when	O
relevant	O
new	O
Web	O
standards	O
continue	O
to	O
be	O
added	O
to	O
the	O
engine	B-Application
.	O
</s>
