<s>
LXR	B-Application
Cross	I-Application
Referencer	I-Application
,	O
usually	O
known	O
as	O
LXR	O
,	O
is	O
a	O
general-purpose	O
source	O
code	O
indexer	O
and	O
cross-referencer	O
for	O
code	B-General_Concept
comprehension	I-General_Concept
that	O
provides	O
web-based	O
browsing	O
of	O
source	O
code	O
,	O
with	O
links	O
to	O
the	O
definition	O
and	O
usage	O
of	O
any	O
identifier	O
.	O
</s>
<s>
LXR	O
was	O
born	O
from	O
a	O
need	O
for	O
a	O
tool	O
to	O
keep	O
a	O
synthetic	O
eye	O
on	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
during	O
its	O
development	O
(	O
whence	O
its	O
original	O
name	O
:	O
LXR	O
stood	O
for	O
"	O
Linux	B-Operating_System
Cross-Referencer	O
"	O
)	O
.	O
</s>
<s>
Two	O
Norwegian	O
students	O
,	O
Arne	O
Georg	O
Gleditsch	O
and	O
Per	O
Kristian	O
Gjermshus	O
,	O
curious	O
about	O
Linux	B-Operating_System
architecture	I-Operating_System
,	O
began	O
writing	O
a	O
small	O
program	O
displaying	O
its	O
files	O
through	O
a	O
web-browser	B-Application
and	O
showing	O
variables	O
usages	O
after	O
a	O
click	O
on	O
the	O
name	O
.	O
</s>
<s>
Aware	O
of	O
general	O
interest	O
,	O
they	O
posted	O
it	O
rapidly	O
on	O
SourceForge	B-Application
(	O
as	O
early	O
as	O
1994	O
?	O
</s>
<s>
With	O
these	O
characteristics	O
,	O
LXR	O
is	O
a	O
typical	O
SourceForge-hosted	O
project	O
but	O
exhibits	O
an	O
exceptional	O
life	O
duration	O
among	O
small	O
projects	O
.	O
</s>
<s>
Linux	B-Operating_System
Journal	O
.	O
</s>
<s>
However	O
,	O
when	O
collecting	O
references	O
to	O
LXR	O
on	O
the	O
Internet	O
,	O
there	O
is	O
ambiguity	O
between	O
the	O
tool	O
itself	O
and	O
instances	O
of	O
LXR	O
displaying	O
indexed	O
source	O
code	O
(	O
since	O
many	O
sites	O
use	O
"	O
LXR	O
"	O
in	O
its	O
original	O
sense	O
of	O
"	O
Linux	B-Operating_System
Cross-Referencer	O
"	O
)	O
.	O
</s>
<s>
After	O
adopting	O
LXR	O
to	O
index	O
the	O
source	O
code	O
for	O
the	O
Mozilla	B-Language
Application	I-Language
Suite	I-Language
,	O
Mozilla	B-Operating_System
forked	O
LXR	O
to	O
into	O
MXR	O
(	O
the	O
Mozilla	B-Operating_System
Cross	O
Reference	O
)	O
.	O
</s>
<s>
MXR	O
was	O
forked	O
in	O
order	O
to	O
meet	O
the	O
needs	O
of	O
Mozilla	B-Operating_System
development	O
,	O
namely	O
code	O
navigation	O
of	O
a	O
mixed	O
C++	B-Language
and	O
JavaScript	B-Language
codebase	O
.	O
</s>
<s>
After	O
years	O
of	O
MXR	O
use	O
,	O
Mozilla	B-Operating_System
began	O
work	O
on	O
a	O
new	O
tool	O
with	O
a	O
focus	O
on	O
better	O
static	O
analysis	O
and	O
a	O
dynamic	O
Ajax	B-General_Concept
UI	O
.	O
</s>
<s>
After	O
DXR	O
reached	O
maturity	O
,	O
the	O
MXR	O
instance	O
at	O
mxr.mozilla.org	O
was	O
decommissioned	O
.	O
</s>
<s>
The	O
design	O
choices	O
include	O
interpreted	O
languages	O
(	O
such	O
as	O
Java	B-Language
or	O
JavaScript	B-Language
)	O
barring	O
or	O
strict	O
HTML	B-Language
4.01	I-Language
conformance	O
.	O
</s>
<s>
Least-effort	O
principle	O
forbids	O
tool	O
programming	O
if	O
it	O
already	O
exists	O
(	O
at	O
least	O
as	O
open	B-Application
source	I-Application
)	O
.	O
</s>
<s>
This	O
results	O
in	O
web	B-Application
browser	I-Application
usage	O
for	O
display	O
(	O
HTML	B-Language
and	O
CSS	B-Language
allow	O
for	O
fancy	O
page	O
lay-out	O
)	O
,	O
definitions	O
and	O
references	O
stored	O
in	O
an	O
available	O
relational	O
data	O
base	O
and	O
file	O
parsing	O
with	O
Exuberant	O
ctags	O
tool	O
.	O
</s>
<s>
LXR	O
is	O
written	O
in	O
Perl	B-Language
,	O
handy	O
choice	O
for	O
CGI	B-Language
scripts	I-Language
,	O
but	O
not	O
really	O
fit	O
for	O
lexical	O
or	O
syntactic	O
parsing	O
.	O
</s>
<s>
several	O
database	O
choices	O
:	O
MySQL	B-Application
,	O
PostgreSQL	B-Application
,	O
SQLite	B-Language
or	O
Oracle	B-General_Concept
,	O
</s>
<s>
choices	O
for	O
full	B-Application
text	I-Application
search	I-Application
between	O
Glimpse	O
and	O
SWISH-E	B-Application
,	O
</s>
<s>
free	O
choice	O
for	O
HTTP	O
server	O
provided	O
it	O
can	O
execute	O
CGI	B-Language
scripts	I-Language
(	O
instructions	O
are	O
given	O
for	O
Apache	B-Application
,	O
Cherokee	B-Language
,	O
lighttpd	B-Protocol
,	O
Nginx	B-Operating_System
and	O
thttpd	B-Language
)	O
,	O
</s>
<s>
source-file	O
stored	O
in	O
real	O
directory	B-Application
or	O
in	O
version	B-Architecture
management	I-Architecture
system	I-Architecture
repository	O
(	O
choice	O
between	O
CVS	B-Application
,	O
Git	B-Application
,	O
Mercurial	B-Protocol
and	O
Subversion	B-Application
)	O
.	O
</s>
<s>
The	O
different	O
source	O
code	O
versions	O
are	O
implemented	O
as	O
sub-directories	O
.	O
</s>
<s>
An	O
alternative	O
stores	O
source	O
code	O
in	O
a	O
version	B-Architecture
management	I-Architecture
system	I-Architecture
.	O
</s>
<s>
Afterwards	O
,	O
all	O
is	O
needed	O
is	O
to	O
launch	O
a	O
web	B-Application
browser	I-Application
with	O
an	O
URL	O
corresponding	O
to	O
the	O
source	O
code	O
and	O
navigate	O
across	O
files	O
through	O
the	O
hyperlinks	O
associated	O
to	O
identifiers	O
.	O
</s>
<s>
Two	O
versions	O
of	O
the	O
same	O
file	O
can	O
be	O
compared	O
side	O
by	O
side	O
with	O
differences	O
visually	O
enhanced	O
(	O
through	O
diff	B-Application
command	O
launched	O
by	O
LXR	O
)	O
.	O
</s>
<s>
To	O
work	O
around	O
the	O
indexing	O
phase	O
limitations	O
,	O
any	O
character	O
sequence	O
may	O
be	O
(	O
full	B-Application
text	I-Application
)	O
searched	O
at	O
the	O
cost	O
of	O
an	O
extensive	O
source	O
files	O
traversal	O
.	O
</s>
<s>
An	O
advanced	O
user	O
may	O
change	O
LXR	O
layout	O
and	O
rendering	O
through	O
customizing	O
page	O
templates	O
(	O
written	O
in	O
HTML	B-Language
)	O
and	O
cascading	B-Language
style	I-Language
sheet	I-Language
(	O
CSS	B-Language
)	O
.	O
</s>
