<s>
xpra	B-Application
,	O
abbreviated	O
from	O
X	B-Operating_System
Persistent	O
Remote	O
Applications	O
,	O
is	O
a	O
set	O
of	O
software	O
utilities	O
that	O
run	O
X	B-Operating_System
clients	O
,	O
typically	O
on	O
a	O
remote	O
host	O
,	O
and	O
direct	O
their	O
display	O
to	O
the	O
local	O
machine	O
without	O
the	O
X	B-Operating_System
clients	O
closing	O
or	O
losing	O
any	O
state	O
in	O
case	O
the	O
network	O
connection	O
between	O
the	O
local	O
machine	O
and	O
the	O
remote	O
host	O
is	O
lost	O
.	O
</s>
<s>
Xpra	B-Application
differs	O
from	O
standard	O
X	B-Operating_System
forwarding	O
primarily	O
in	O
allowing	O
disconnection	O
and	O
reconnection	O
without	O
disrupting	O
the	O
forwarded	O
application	O
.	O
</s>
<s>
It	O
also	O
differs	O
from	O
VNC	B-Protocol
and	O
similar	O
remote	O
display	O
technologies	O
in	O
being	O
rootless	O
,	O
so	O
applications	O
forwarded	O
by	O
Xpra	B-Application
appear	O
on	O
the	O
local	O
desktop	O
as	O
normal	O
windows	O
managed	O
by	O
the	O
local	O
window	B-Application
manager	I-Application
,	O
rather	O
than	O
being	O
all	O
"	O
trapped	O
in	O
a	O
box	O
together	O
"	O
.	O
</s>
<s>
Xpra	B-Application
also	O
uses	O
a	O
custom	O
protocol	O
that	O
is	O
self-tuning	O
and	O
relatively	O
latency-insensitive	O
,	O
and	O
thus	O
is	O
usable	O
over	O
worse	O
links	O
than	O
standard	O
X	B-Operating_System
.	O
</s>
<s>
The	O
original	O
inspiration	O
for	O
making	O
Xpra	B-Application
came	O
from	O
the	O
original	O
author	O
's	O
experience	O
of	O
attempting	O
to	O
use	O
various	O
setups	O
based	O
on	O
NX	B-Application
technology	I-Application
.	O
</s>
<s>
Xpra	B-Application
connects	O
as	O
a	O
compositing	B-Operating_System
window	I-Operating_System
manager	I-Operating_System
to	O
an	O
Xvfb	B-Device
display	O
server	O
.	O
</s>
<s>
However	O
,	O
instead	O
of	O
combining	O
the	O
window	O
images	O
to	O
present	O
on	O
the	O
screen	O
,	O
it	O
directs	O
the	O
window	O
images	O
into	O
a	O
network	O
connection	O
to	O
the	O
Xpra	B-Application
client	O
,	O
where	O
they	O
are	O
displayed	O
on	O
the	O
remote	O
screen	O
.	O
</s>
<s>
The	O
Xpra	B-Application
server	O
also	O
supports	O
direct	O
attachment	O
,	O
which	O
makes	O
it	O
behave	O
as	O
a	O
persistent	O
application	O
server	O
,	O
for	O
example	O
in	O
the	O
case	O
where	O
there	O
is	O
only	O
an	O
X	B-Operating_System
server	O
available	O
at	O
the	O
remote	O
end	O
.	O
</s>
<s>
Xpra	B-Application
also	O
acts	O
as	O
a	O
window	B-Application
manager	I-Application
for	O
the	O
X	B-Operating_System
server	O
it	O
is	O
running	O
against	O
,	O
but	O
it	O
does	O
not	O
actually	O
have	O
any	O
window	B-Application
manager	I-Application
policy	O
built	O
into	O
it	O
.	O
</s>
<s>
Instead	O
,	O
it	O
takes	O
all	O
the	O
window	B-Application
management	I-Application
requests	O
from	O
the	O
applications	O
,	O
sends	O
them	O
over	O
the	O
wire	O
to	O
the	O
client	O
,	O
which	O
then	O
issues	O
those	O
same	O
requests	O
on	O
the	O
real	O
display	O
,	O
waits	O
for	O
further	O
answer	O
the	O
real	O
window	B-Application
manager	I-Application
gives	O
,	O
and	O
then	O
forwards	O
that	O
answer	O
back	O
to	O
the	O
Xpra	B-Application
server	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
normal	O
Xpra	B-Application
client	O
,	O
it	O
also	O
supports	O
using	O
an	O
HTML	O
5	O
capable	O
web	O
browser	O
as	O
a	O
client	O
.	O
</s>
