<s>
The	O
FSEvents	B-Operating_System
API	B-General_Concept
in	O
macOS	B-Application
allows	O
applications	O
to	O
register	O
for	O
notifications	O
of	O
changes	O
to	O
a	O
given	O
directory	B-Application
tree	I-Application
.	O
</s>
<s>
Whenever	O
the	O
filesystem	O
is	O
changed	O
,	O
the	O
kernel	O
passes	O
notifications	O
via	O
the	O
special	O
device	B-Application
file	I-Application
/dev/fsevents	O
to	O
a	O
userspace	B-Operating_System
process	O
called	O
fseventsd	O
.	O
</s>
<s>
This	O
process	O
combines	O
multiple	O
changes	O
to	O
a	O
single	O
directory	B-Application
tree	I-Application
that	O
occur	O
within	O
a	O
short	O
period	O
of	O
time	O
,	O
then	O
notifies	O
applications	O
that	O
have	O
registered	O
for	O
changes	O
to	O
the	O
affected	O
directory	B-Application
.	O
</s>
<s>
Until	O
Mac	B-Application
OS	I-Application
X	O
10.7	O
,	O
FSEvents	B-Operating_System
did	O
not	O
"	O
watch	O
"	O
the	O
filesystem	O
,	O
such	O
as	O
Linux	B-Application
's	O
inotify	B-Application
:	O
the	O
API	B-General_Concept
provided	O
no	O
notifications	O
for	O
changes	O
to	O
individual	O
files	O
.	O
</s>
<s>
An	O
application	O
was	O
able	O
to	O
register	O
to	O
receive	O
changes	O
to	O
a	O
given	O
directory	B-Application
,	O
and	O
had	O
to	O
determine	O
for	O
itself	O
which	O
file	O
or	O
files	O
were	O
changed	O
.	O
</s>
<s>
Mac	B-Application
OS	I-Application
X	O
10.7	O
(	O
Lion	O
)	O
added	O
the	O
ability	O
to	O
register	O
for	O
file	O
modification	O
notifications	O
.	O
</s>
