<s>
In	O
computer	B-Language
language	I-Language
design	O
,	O
stropping	B-Application
is	O
a	O
method	O
of	O
explicitly	O
marking	O
letter	O
sequences	O
as	O
having	O
a	O
special	O
property	O
,	O
such	O
as	O
being	O
a	O
keyword	O
,	O
or	O
a	O
certain	O
type	O
of	O
variable	O
or	O
storage	O
location	O
,	O
and	O
thus	O
inhabiting	O
a	O
different	O
namespace	O
from	O
ordinary	O
names	O
(	O
"	O
identifiers	O
"	O
)	O
,	O
in	O
order	O
to	O
avoid	O
clashes	O
.	O
</s>
<s>
Stropping	B-Application
is	O
not	O
used	O
in	O
most	O
modern	O
languages	O
–	O
instead	O
,	O
keywords	O
are	O
reserved	O
words	O
and	O
cannot	O
be	O
used	O
as	O
identifiers	O
.	O
</s>
<s>
Stropping	B-Application
allows	O
the	O
same	O
letter	O
sequence	O
to	O
be	O
used	O
both	O
as	O
a	O
keyword	O
and	O
as	O
an	O
identifier	O
,	O
and	O
simplifies	O
parsing	O
in	O
that	O
case	O
–	O
for	O
example	O
allowing	O
a	O
variable	O
named	O
if	O
without	O
clashing	O
with	O
the	O
keyword	O
if	O
.	O
</s>
<s>
Stropping	B-Application
is	O
primarily	O
associated	O
with	O
ALGOL	B-Language
and	O
related	O
languages	O
in	O
the	O
1960s	O
.	O
</s>
<s>
The	O
method	O
of	O
stropping	B-Application
and	O
the	O
term	O
"	O
stropping	B-Application
"	O
arose	O
in	O
the	O
development	O
of	O
ALGOL	B-Language
in	O
the	O
1960s	O
,	O
where	O
it	O
was	O
used	O
to	O
represent	O
typographical	O
distinctions	O
(	O
boldface	O
and	O
underline	O
)	O
found	O
in	O
the	O
publication	O
language	O
which	O
could	O
not	O
directly	O
be	O
represented	O
in	O
the	O
hardware	O
language	O
–	O
a	O
typewriter	O
could	O
have	O
bold	O
characters	O
,	O
but	O
in	O
encoding	O
in	O
punch	O
cards	O
,	O
there	O
were	O
no	O
bold	O
characters	O
.	O
</s>
<s>
The	O
term	O
"	O
stropping	B-Application
"	O
arose	O
in	O
ALGOL	B-Language
60	I-Language
,	O
from	O
"	O
apostrophe	B-Language
"	O
,	O
as	O
some	O
implementations	O
of	O
ALGOL	B-Language
60	I-Language
used	O
apostrophes	B-Language
around	O
text	O
to	O
indicate	O
boldface	O
,	O
such	O
as	O
'	O
if	O
 '	O
to	O
represent	O
the	O
keyword	O
if	O
.	O
</s>
<s>
Stropping	B-Application
is	O
also	O
important	O
in	O
ALGOL	B-Language
68	I-Language
,	O
where	O
multiple	O
methods	O
of	O
stropping	B-Application
,	O
known	O
as	O
"	O
stropping	B-Application
regimes	O
"	O
,	O
are	O
used	O
;	O
the	O
original	O
matched	O
apostrophes	B-Language
from	O
ALGOL	B-Language
60	I-Language
was	O
not	O
widely	O
used	O
,	O
with	O
a	O
leading	O
period	O
or	O
uppercase	O
being	O
more	O
common	O
,	O
as	O
in	O
.IF	O
or	O
IF	O
and	O
the	O
term	O
"	O
stropping	B-Application
"	O
was	O
applied	O
to	O
all	O
of	O
these	O
.	O
</s>
<s>
A	O
range	O
of	O
different	O
syntaxes	O
for	O
stropping	B-Application
have	O
been	O
used	O
:	O
</s>
<s>
Algol	B-Language
60	I-Language
commonly	O
used	O
only	O
the	O
convention	O
of	O
single	O
quotes	O
around	O
the	O
word	O
,	O
generally	O
as	O
apostrophes	B-Language
,	O
whence	O
the	O
name	O
"	O
stropping	B-Application
"	O
(	O
e.g.	O
</s>
<s>
In	O
fact	O
it	O
was	O
often	O
the	O
case	O
that	O
several	O
stropping	B-Application
conventions	O
might	O
be	O
in	O
use	O
within	O
one	O
language	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
ALGOL	B-Language
68	I-Language
,	O
the	O
choice	O
of	O
stropping	B-Application
convention	O
can	O
be	O
specified	O
by	O
a	O
compiler	B-Language
directive	O
(	O
in	O
ALGOL	B-Language
terminology	O
,	O
a	O
"	O
pragmat	O
"	O
)	O
,	O
namely	O
POINT	O
,	O
UPPER	O
,	O
QUOTE	O
,	O
or	O
RES	O
:	O
</s>
<s>
The	O
various	O
rules	O
regimes	O
are	O
a	O
lexical	B-Application
specification	I-Application
for	O
stropped	O
characters	O
,	O
though	O
in	O
some	O
cases	O
these	O
have	O
simple	O
interpretations	O
:	O
in	O
the	O
single	O
apostrophe	B-Language
and	O
dot	O
regimes	O
,	O
the	O
first	O
character	O
is	O
functioning	O
as	O
an	O
escape	B-Algorithm
character	I-Algorithm
,	O
while	O
in	O
the	O
matched	O
apostrophes	B-Language
regime	O
the	O
apostrophes	B-Language
are	O
functioning	O
as	O
delimiters	B-Algorithm
,	O
as	O
in	O
string	B-Language
literals	I-Language
.	O
</s>
<s>
Atlas	O
Autocode	O
had	O
the	O
choice	O
of	O
three	O
:	O
keywords	O
could	O
be	O
underlined	O
using	O
backspace	O
and	O
overstrike	O
on	O
a	O
Flexowriter	B-Application
keyboard	O
,	O
they	O
could	O
be	O
introduced	O
by	O
a	O
%percent	O
%symbol	O
,	O
or	O
they	O
could	O
be	O
typed	O
in	O
UPPER	O
CASE	O
with	O
no	O
delimiting	B-Algorithm
character	O
(	O
"	O
uppercasedelimiters	O
"	O
mode	O
,	O
in	O
which	O
case	O
all	O
variables	O
had	O
to	O
be	O
in	O
lower	O
case	O
)	O
.	O
</s>
<s>
Algol	B-Language
60	I-Language
on	O
the	O
Elliott	B-Device
803	I-Device
and	O
Elliott	B-Device
503	I-Device
computers	O
used	O
underlining	O
.	O
</s>
<s>
The	O
Flexowriters	B-Application
(	O
producing	O
punched	O
paper	O
tape	O
)	O
had	O
a	O
non-movement	O
key	O
(	O
underline	O
_	O
)	O
so	O
that	O
typing	O
_b_e_g_i_n	O
produced	O
begin	O
which	O
was	O
very	O
readable	O
.	O
</s>
<s>
The	O
Kidsgrove	O
compiler	B-Language
for	O
Algol	B-Language
60	I-Language
on	O
the	O
English	B-Device
Electric	I-Device
KDF9	I-Device
appears	O
to	O
have	O
used	O
at	O
least	O
two	O
other	O
stropping	B-Application
conventions	O
in	O
addition	O
to	O
quotation	O
marks	O
:	O
and	O
.	O
</s>
<s>
ALGOL	B-General_Concept
68RS	I-General_Concept
programs	O
are	O
allowed	O
the	O
use	O
of	O
several	O
stropping	B-Application
variants	O
,	O
even	O
within	O
the	O
one	O
language	O
processor	O
.	O
</s>
<s>
Note	O
the	O
leading	O
pr	O
(	O
abbreviation	O
of	O
pragmat	O
)	O
directive	O
,	O
which	O
is	O
itself	O
stropped	O
in	O
POINT	O
or	O
quote	O
style	O
,	O
and	O
the	O
for	O
comment	O
(	O
from	O
""	O
)	O
–	O
see	O
ALGOL	B-Language
68	I-Language
:	O
pr	O
&	O
co	O
:	O
Pragmats	O
and	O
Comments	O
for	O
details	O
.	O
</s>
<s>
are	O
also	O
used	O
in	O
combined	O
tests	O
in	O
IF	O
and	O
IFF	O
statements	O
in	O
batch	O
files	O
run	O
under	O
JP	B-Application
Software	I-Application
's	O
command	O
line	O
processors	O
like	O
4DOS	B-Application
,	O
4OS2	B-Application
,	O
and	O
4NT	B-Application
/	I-Application
Take	I-Application
Command	I-Application
.	O
</s>
<s>
Most	O
modern	O
computer	B-Language
languages	I-Language
do	O
not	O
use	O
stropping	B-Application
,	O
with	O
two	O
notable	O
exceptions	O
:	O
</s>
<s>
The	O
use	O
of	O
many	O
languages	O
in	O
Microsoft	O
's	O
.NET	B-Application
Common	O
Language	O
Infrastructure	O
(	O
CLI	O
)	O
requires	O
a	O
way	O
to	O
use	O
variables	O
in	O
a	O
different	O
language	O
that	O
may	O
be	O
keywords	O
in	O
a	O
calling	O
language	O
.	O
</s>
<s>
This	O
is	O
sometimes	O
done	O
by	O
prefixes	O
,	O
such	O
as	O
@	O
in	O
C#	O
,	O
or	O
enclosing	O
the	O
identifier	O
in	O
brackets	O
,	O
in	O
Visual	B-Language
Basic.NET	I-Language
.	O
</s>
<s>
A	O
second	O
major	O
example	O
is	O
in	O
many	O
implementations	O
of	O
Structured	B-Language
Query	I-Language
Language	I-Language
.	O
</s>
<s>
In	O
those	O
languages	O
reserved	O
words	O
can	O
be	O
used	O
as	O
column	O
,	O
table	O
,	O
or	O
variable	O
names	O
by	O
lexically	O
delimiting	B-Algorithm
them	O
.	O
</s>
<s>
The	O
standard	O
specifies	O
enclosing	O
reserved	O
words	O
in	O
double	O
quotes	O
,	O
but	O
in	O
practice	O
the	O
exact	O
mechanism	O
varies	O
by	O
implementation	O
;	O
MySQL	B-Application
,	O
for	O
example	O
,	O
allows	O
reserved	O
words	O
to	O
be	O
used	O
in	O
other	O
contexts	O
by	O
enclosing	O
them	O
in	O
backticks	O
,	O
and	O
Microsoft	B-Application
SQL	I-Application
Server	I-Application
uses	O
square	O
brackets	O
.	O
</s>
<s>
Stropping	B-Application
can	O
also	O
be	O
used	O
in	O
the	O
Nim	B-Application
programming	I-Application
language	I-Application
.	O
</s>
<s>
In	O
Nim	B-Application
,	O
a	O
reserved	O
word	O
can	O
be	O
used	O
as	O
an	O
identifier	O
by	O
enclosing	O
it	O
in	O
backticks	O
.	O
</s>
<s>
For	O
example	O
,	O
Web	B-Protocol
IDL	I-Protocol
uses	O
a	O
leading	O
underscore	O
_	O
to	O
strop	O
identifiers	O
that	O
otherwise	O
collide	O
with	O
reserved	O
words	O
:	O
the	O
value	O
of	O
the	O
identifier	O
strips	O
this	O
leading	O
underscore	O
,	O
making	O
this	O
stropping	B-Application
,	O
rather	O
than	O
a	O
naming	O
convention	O
.	O
</s>
<s>
In	O
a	O
compiler	B-Language
frontend	O
,	O
originally	O
occurred	O
during	O
an	O
initial	O
line	O
reconstruction	O
phase	O
,	O
which	O
also	O
eliminated	O
whitespace	O
.	O
</s>
<s>
This	O
was	O
then	O
followed	O
by	O
scannerless	B-Application
parsing	I-Application
(	O
no	O
tokenization	O
)	O
;	O
this	O
was	O
standard	O
in	O
the	O
1960s	O
,	O
notably	O
for	O
ALGOL	B-Language
.	O
</s>
<s>
In	O
modern	O
use	O
,	O
is	O
generally	O
done	O
as	O
part	O
of	O
lexical	B-Application
analysis	I-Application
.	O
</s>
<s>
This	O
is	O
clear	O
if	O
one	O
distinguishes	O
the	O
lexer	B-Application
into	O
two	O
phases	O
of	O
scanner	B-Application
and	O
evaluator	O
:	O
the	O
scanner	B-Application
categorizes	O
the	O
stropped	O
sequence	O
into	O
the	O
correct	O
category	O
,	O
and	O
then	O
the	O
evaluator	O
when	O
calculating	O
the	O
value	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
a	O
language	O
where	O
an	O
initial	O
underscore	O
is	O
used	O
to	O
strop	O
identifiers	O
to	O
avoid	O
collisions	O
with	O
reserved	O
words	O
,	O
the	O
sequence	O
_if	O
would	O
be	O
categorized	O
as	O
an	O
identifier	O
(	O
not	O
as	O
the	O
reserved	O
word	O
if	O
)	O
by	O
the	O
scanner	B-Application
,	O
and	O
then	O
the	O
evaluator	O
would	O
give	O
this	O
the	O
value	O
if	O
,	O
yielding	O
(	O
Identifier	O
,	O
if	O
)	O
as	O
the	O
token	O
type	O
and	O
value	O
.	O
</s>
<s>
Strictly	O
speaking	O
,	O
stropping	B-Application
consists	O
of	O
different	O
representations	O
of	O
the	O
same	O
name	O
(	O
value	O
)	O
in	O
different	O
namespaces	O
,	O
and	O
occurs	O
at	O
the	O
tokenization	O
stage	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
ALGOL	B-Language
60	I-Language
with	O
matched	O
apostrophe	B-Language
stropping	B-Application
,	O
'	O
if	O
 '	O
is	O
tokenized	O
as	O
(	O
Keyword	O
,	O
if	O
)	O
,	O
while	O
if	O
is	O
tokenized	O
as	O
(	O
Identifier	O
,	O
if	O
)	O
–	O
same	O
value	O
in	O
different	O
token	O
classes	O
.	O
</s>
<s>
Using	O
uppercase	O
for	O
keywords	O
remains	O
in	O
use	O
as	O
a	O
convention	O
for	O
writing	O
grammars	O
for	O
lexing	B-Application
and	O
parsing	O
–	O
tokenizing	O
the	O
reserved	O
word	O
if	O
as	O
the	O
token	O
class	O
IF	O
,	O
and	O
then	O
representing	O
an	O
if-then-else	O
clause	O
by	O
the	O
phrase	O
IF	O
Expression	O
THEN	O
Statement	O
ELSE	O
Statement	O
where	O
uppercase	O
terms	O
are	O
keywords	O
and	O
capitalized	O
terms	O
are	O
nonterminal	O
symbols	O
in	O
a	O
production	O
rule	O
(	O
terminal	O
symbols	O
are	O
denoted	O
by	O
lowercase	O
terms	O
,	O
such	O
as	O
identifier	O
or	O
integer	O
,	O
for	O
an	O
integer	O
literal	O
)	O
.	O
</s>
<s>
These	O
names	O
may	O
be	O
interpreted	O
by	O
the	O
compiler	B-Language
and	O
have	O
some	O
effect	O
,	O
though	O
this	O
is	O
generally	O
done	O
at	O
the	O
semantic	O
analysis	O
phase	O
,	O
not	O
the	O
tokenization	O
phase	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
Python	O
,	O
a	O
single	O
leading	O
underscore	O
is	O
a	O
weak	O
private	O
indicator	O
,	O
and	O
affects	O
which	O
identifiers	O
are	O
imported	O
on	O
module	O
import	O
,	O
while	O
a	O
double	O
leading	O
underscore	O
(	O
and	O
no	O
more	O
than	O
one	O
trailing	O
underscore	O
)	O
on	O
a	O
class	O
attribute	O
invokes	O
name	B-Language
mangling	I-Language
.	O
</s>
<s>
While	O
modern	O
languages	O
generally	O
use	O
reserved	O
words	O
rather	O
than	O
stropping	B-Application
to	O
distinguish	O
keywords	O
from	O
identifiers	O
–	O
e.g.	O
,	O
making	O
if	O
reserved	O
–	O
they	O
also	O
frequently	O
reserve	O
a	O
syntactic	O
class	O
of	O
identifiers	O
as	O
keywords	O
,	O
yielding	O
representations	O
which	O
can	O
be	O
interpreted	O
as	O
a	O
stropping	B-Application
regime	O
,	O
but	O
instead	O
have	O
the	O
semantics	O
of	O
reserved	O
words	O
.	O
</s>
<s>
While	O
this	O
is	O
superficially	O
similar	O
to	O
stropping	B-Application
,	O
the	O
semantics	O
are	O
different	O
.	O
</s>
<s>
In	O
stropping	B-Application
(	O
by	O
prefixing	O
keywords	O
by	O
__	O
)	O
,	O
the	O
string	O
__foo	O
represents	O
the	O
keyword	O
foo	O
in	O
a	O
separate	O
keyword	O
namespace	O
.	O
</s>
<s>
Thus	O
using	O
reserved	O
words	O
,	O
the	O
tokens	O
for	O
__foo	O
and	O
foo	O
are	O
(	O
identifier	O
,	O
__foo	O
)	O
and	O
(	O
identifier	O
,	O
foo	O
)	O
–	O
different	O
values	O
in	O
the	O
same	O
category	O
–	O
while	O
in	O
stropping	B-Application
the	O
tokens	O
for	O
__foo	O
and	O
foo	O
are	O
(	O
keyword	O
,	O
foo	O
)	O
and	O
(	O
identifier	O
,	O
foo	O
)	O
–	O
same	O
values	O
in	O
different	O
categories	O
.	O
</s>
<s>
Name	B-Language
mangling	I-Language
also	O
addresses	O
name	O
clashes	O
by	O
renaming	O
identifiers	O
,	O
but	O
does	O
this	O
much	O
later	O
in	O
compilation	B-Language
,	O
during	O
semantic	O
analysis	O
,	O
not	O
during	O
tokenization	O
.	O
</s>
<s>
These	O
are	O
common	O
in	O
Perl	B-Language
,	O
Ruby	B-Language
,	O
and	O
various	O
other	O
languages	O
to	O
identify	O
characteristics	O
of	O
variables/constants	O
:	O
Perl	B-Language
to	O
designate	O
the	O
type	O
of	O
variable	O
,	O
Ruby	B-Language
both	O
to	O
distinguish	O
variables	O
from	O
constants	O
and	O
to	O
indicate	O
scope	O
.	O
</s>
<s>
Stropping	B-Application
is	O
used	O
in	O
computer	O
programming	O
languages	O
to	O
make	O
the	O
compiler	B-Language
's	O
(	O
or	O
more	O
strictly	O
,	O
the	O
parser	B-Language
's	O
)	O
job	O
easier	O
,	O
i.e.	O
</s>
<s>
Placing	O
important	O
words	O
in	O
bold	O
,	O
such	O
as	O
the	O
very	O
first	O
mention	O
of	O
stropping	B-Application
at	O
the	O
head	O
of	O
this	O
page	O
,	O
because	O
defining	O
stropping	B-Application
is	O
the	O
very	O
purpose	O
of	O
the	O
page	O
.	O
</s>
<s>
This	O
is	O
commonly	O
used	O
in	O
science	O
fiction	O
and	O
fantasy	B-Application
when	O
introducing	O
invented	O
plants	O
,	O
foods	O
,	O
creatures	O
;	O
in	O
travelogue	O
and	O
historical	O
writing	O
when	O
describing	O
unfamiliar	O
foreign	O
words	O
;	O
and	O
so	O
on	O
.	O
</s>
