<s>
The	O
Standard	B-Language
Generalized	I-Language
Markup	I-Language
Language	I-Language
(	O
SGML	B-Language
;	O
ISO	O
8879:1986	O
)	O
is	O
a	O
standard	O
for	O
defining	O
generalized	B-Application
markup	I-Application
languages	I-Application
for	O
documents	O
.	O
</s>
<s>
ISO	B-Language
8879	I-Language
Annex	O
A.1	O
states	O
that	O
generalized	O
markup	O
is	O
"	O
based	O
on	O
two	O
postulates	O
"	O
:	O
</s>
<s>
DocBook	B-Protocol
SGML	B-Language
and	O
LinuxDoc	B-Operating_System
are	O
examples	O
which	O
used	O
SGML	B-Language
tools	O
.	O
</s>
<s>
SGML	B-Language
is	O
an	O
ISO	O
standard	O
:	O
"	O
ISO	O
8879:1986	O
Information	O
processing	O
–	O
Text	O
and	O
office	O
systems	O
–	O
Standard	B-Language
Generalized	I-Language
Markup	I-Language
Language	I-Language
(	O
SGML	B-Language
)	O
"	O
,	O
of	O
which	O
there	O
are	O
three	O
versions	O
:	O
</s>
<s>
Original	O
SGML	B-Language
,	O
which	O
was	O
accepted	O
in	O
October	O
1986	O
,	O
followed	O
by	O
a	O
minor	O
Technical	O
Corrigendum	O
.	O
</s>
<s>
SGML	B-Language
(	O
ENR	O
)	O
,	O
in	O
1996	O
,	O
resulted	O
from	O
a	O
Technical	O
Corrigendum	O
to	O
add	O
extended	O
naming	O
rules	O
allowing	O
arbitrary-language	O
and	O
-script	O
markup	O
.	O
</s>
<s>
SGML	B-Language
(	O
ENR+WWW	O
or	O
WebSGML	O
)	O
,	O
in	O
1998	O
,	O
resulted	O
from	O
a	O
to	O
better	O
support	O
XML	B-Protocol
and	O
WWW	O
requirements	O
.	O
</s>
<s>
SGML	B-Language
is	O
part	O
of	O
a	O
trio	O
of	O
enabling	O
ISO	O
standards	O
for	O
electronic	B-Protocol
documents	I-Protocol
developed	O
by	O
ISO/IEC	O
JTC	O
1/SC	O
34	O
(	O
ISO/IEC	O
Joint	O
Technical	O
Committee	O
1	O
,	O
Subcommittee	O
34	O
–	O
Document	O
description	O
and	O
processing	O
languages	O
)	O
:	O
</s>
<s>
SGML	B-Language
was	O
reworked	O
in	O
1998	O
into	O
XML	B-Protocol
,	O
a	O
successful	O
profile	O
of	O
SGML	B-Language
.	O
</s>
<s>
Full	O
SGML	B-Language
is	O
rarely	O
found	O
or	O
used	O
in	O
new	O
projects	O
.	O
</s>
<s>
DSSSL	B-Language
(	O
ISO/IEC	B-Language
10179	I-Language
)	O
–	O
Document	O
processing	O
and	O
styling	O
language	O
based	O
on	O
Scheme	B-Language
.	O
</s>
<s>
DSSSL	B-Language
was	O
reworked	O
into	O
W3C	O
XSLT	B-Application
and	O
XSL-FO	B-Language
which	O
use	O
an	O
XML	B-Protocol
syntax	O
.	O
</s>
<s>
Nowadays	O
,	O
DSSSL	B-Language
is	O
rarely	O
used	O
in	O
new	O
projects	O
apart	O
from	O
Linux	B-Application
documentation	O
.	O
</s>
<s>
HyTime	B-Language
–	O
Generalized	O
hypertext	O
and	O
scheduling	O
.	O
</s>
<s>
HyTime	B-Language
was	O
partially	O
reworked	O
into	O
W3C	O
XLink	O
.	O
</s>
<s>
HyTime	B-Language
is	O
rarely	O
used	O
in	O
new	O
projects	O
.	O
</s>
<s>
SGML	B-Language
descended	O
from	O
IBM	O
's	O
Generalized	B-Application
Markup	I-Application
Language	I-Application
(	O
GML	B-Application
)	O
,	O
which	O
Charles	O
Goldfarb	O
,	O
Edward	O
Mosher	O
,	O
and	O
Raymond	O
Lorie	O
developed	O
in	O
the	O
1960s	O
.	O
</s>
<s>
Goldfarb	O
,	O
editor	O
of	O
the	O
international	O
standard	O
,	O
coined	O
the	O
"	O
GML	B-Application
"	O
term	O
using	O
their	O
surname	O
initials	O
.	O
</s>
<s>
Goldfarb	O
also	O
wrote	O
the	O
definitive	O
work	O
on	O
SGML	B-Language
syntax	O
in	O
"	O
The	O
SGML	B-Language
Handbook	O
"	O
.	O
</s>
<s>
The	O
syntax	O
of	O
SGML	B-Language
is	O
closer	O
to	O
the	O
COCOA	O
format	O
.	O
</s>
<s>
As	O
a	O
document	O
markup	O
language	O
,	O
SGML	B-Language
was	O
originally	O
designed	O
to	O
enable	O
the	O
sharing	O
of	O
machine-readable	B-General_Concept
large-project	O
documents	O
in	O
government	O
,	O
law	O
,	O
and	O
industry	O
.	O
</s>
<s>
Many	O
such	O
documents	O
must	O
remain	O
readable	O
for	O
several	O
decades	O
—	O
a	O
long	O
time	O
in	O
the	O
information	B-General_Concept
technology	I-General_Concept
field	O
.	O
</s>
<s>
SGML	B-Language
also	O
was	O
extensively	O
applied	O
by	O
the	O
military	O
,	O
and	O
the	O
aerospace	O
,	O
technical	O
reference	O
,	O
and	O
industrial	O
publishing	O
industries	O
.	O
</s>
<s>
The	O
advent	O
of	O
the	O
XML	B-Protocol
profile	O
has	O
made	O
SGML	B-Language
suitable	O
for	O
widespread	O
application	O
for	O
small-scale	O
,	O
general-purpose	O
use	O
.	O
</s>
<s>
SGML	B-Language
(	O
ENR+WWW	O
)	O
defines	O
two	O
kinds	O
of	O
validity	O
.	O
</s>
<s>
According	O
to	O
the	O
revised	O
Terms	O
and	O
Definitions	O
of	O
ISO	B-Language
8879	I-Language
(	O
from	O
the	O
public	O
draft	O
)	O
:	O
</s>
<s>
A	O
conforming	O
SGML	B-Language
document	O
must	O
be	O
either	O
a	O
type-valid	O
SGML	B-Language
document	O
,	O
a	O
tag-valid	O
SGML	B-Language
document	O
,	O
or	O
both	O
.	O
</s>
<s>
An	O
SGML	B-Language
document	O
in	O
which	O
,	O
for	O
each	O
document	O
instance	O
,	O
there	O
is	O
an	O
associated	O
document	O
type	O
declaration	O
(	O
DTD	O
)	O
to	O
whose	O
DTD	O
that	O
instance	O
conforms	O
.	O
</s>
<s>
An	O
SGML	B-Language
document	O
,	O
all	O
of	O
whose	O
document	O
instances	O
are	O
fully	O
tagged	O
.	O
</s>
<s>
Note	O
:	O
If	O
there	O
is	O
a	O
document	O
type	O
declaration	O
,	O
the	O
instance	O
can	O
be	O
parsed	B-Language
with	O
or	O
without	O
reference	O
to	O
it	O
.	O
</s>
<s>
Tag-validity	O
was	O
introduced	O
in	O
SGML	B-Language
(	O
ENR+WWW	O
)	O
to	O
support	O
XML	B-Protocol
which	O
allows	O
documents	O
with	O
no	O
DOCTYPE	O
declaration	O
but	O
which	O
can	O
be	O
parsed	B-Language
without	O
a	O
grammar	O
,	O
or	O
documents	O
which	O
have	O
a	O
DOCTYPE	O
declaration	O
that	O
makes	O
no	O
XML	B-Protocol
Infoset	O
contributions	O
to	O
the	O
document	O
.	O
</s>
<s>
Integrally	O
stored	O
reflects	O
the	O
XML	B-Protocol
requirement	O
that	O
elements	O
end	O
in	O
the	O
same	O
entity	O
in	O
which	O
they	O
started	O
.	O
</s>
<s>
Reference-free	O
reflects	O
the	O
HTML	B-Language
requirement	O
that	O
entity	O
references	O
are	O
for	O
special	O
characters	O
and	O
do	O
not	O
contain	O
markup	O
.	O
</s>
<s>
SGML	B-Language
validity	O
commentary	O
,	O
especially	O
commentary	O
that	O
was	O
made	O
before	O
1997	O
or	O
that	O
is	O
unaware	O
of	O
SGML	B-Language
(	O
ENR+WWW	O
)	O
,	O
covers	O
type-validity	O
only	O
.	O
</s>
<s>
The	O
SGML	B-Language
emphasis	O
on	O
validity	O
supports	O
the	O
requirement	O
for	O
generalized	O
markup	O
that	O
markup	O
should	O
be	O
rigorous	O
.	O
</s>
<s>
An	O
SGML	B-Language
document	O
may	O
have	O
three	O
parts	O
:	O
</s>
<s>
the	O
SGML	B-Language
Declaration	O
,	O
</s>
<s>
An	O
SGML	B-Language
document	O
may	O
be	O
composed	O
from	O
many	O
entities	B-Language
(	O
discrete	O
pieces	O
of	O
text	O
)	O
.	O
</s>
<s>
In	O
SGML	B-Language
,	O
the	O
entities	B-Language
and	O
element	O
types	O
used	O
in	O
the	O
document	O
may	O
be	O
specified	O
with	O
a	O
DTD	O
,	O
the	O
different	O
character	O
sets	O
,	O
features	O
,	O
delimiter	B-Algorithm
sets	O
,	O
and	O
keywords	O
are	O
specified	O
in	O
the	O
SGML	B-Language
Declaration	O
to	O
create	O
the	O
concrete	O
syntax	O
of	O
the	O
document	O
.	O
</s>
<s>
Although	O
full	O
SGML	B-Language
allows	O
implicit	O
markup	O
and	O
some	O
other	O
kinds	O
of	O
tags	O
,	O
the	O
XML	B-Protocol
specification	I-Protocol
(	O
s4.3.1	O
)	O
states	O
:	O
</s>
<s>
For	O
introductory	O
information	O
on	O
a	O
basic	O
,	O
modern	O
SGML	B-Language
syntax	O
,	O
see	O
XML	B-Protocol
.	O
</s>
<s>
The	O
following	O
material	O
concentrates	O
on	O
features	O
not	O
in	O
XML	B-Protocol
and	O
is	O
not	O
a	O
comprehensive	O
summary	O
of	O
SGML	B-Language
syntax	O
.	O
</s>
<s>
SGML	B-Language
generalizes	O
and	O
supports	O
a	O
wide	O
range	O
of	O
markup	O
languages	O
as	O
found	O
in	O
the	O
mid	O
1980s	O
.	O
</s>
<s>
These	O
ranged	O
from	O
terse	O
Wiki-like	O
syntaxes	O
to	O
RTF-like	O
bracketed	O
languages	O
to	O
HTML-like	O
matching-tag	O
languages	O
.	O
</s>
<s>
SGML	B-Language
did	O
this	O
by	O
a	O
relatively	O
simple	O
default	O
reference	O
concrete	O
syntax	O
augmented	O
with	O
a	O
large	O
number	O
of	O
optional	O
features	O
that	O
could	O
be	O
enabled	O
in	O
the	O
SGML	B-Language
Declaration	O
.	O
</s>
<s>
Not	O
every	O
SGML	B-Language
parser	B-Language
can	O
necessarily	O
process	O
every	O
SGML	B-Language
document	O
.	O
</s>
<s>
Because	O
each	O
processor	O
's	O
System	O
Declaration	O
can	O
be	O
compared	O
to	O
the	O
document	O
's	O
SGML	B-Language
Declaration	O
it	O
is	O
always	O
possible	O
to	O
know	O
whether	O
a	O
document	O
is	O
supported	O
by	O
a	O
particular	O
processor	O
.	O
</s>
<s>
Many	O
SGML	B-Language
features	O
relate	O
to	O
markup	O
minimization	O
.	O
</s>
<s>
Other	O
features	O
relate	O
to	O
concurrent	O
(	O
parallel	O
)	O
markup	O
(	O
CONCUR	O
)	O
,	O
to	O
linking	O
processing	O
attributes	O
(	O
LINK	O
)	O
,	O
and	O
to	O
embedding	O
SGML	B-Language
documents	O
within	O
SGML	B-Language
documents	O
(	O
SUBDOC	O
)	O
.	O
</s>
<s>
The	O
notion	O
of	O
customizable	O
features	O
was	O
not	O
appropriate	O
for	O
Web	O
use	O
,	O
so	O
one	O
goal	O
of	O
XML	B-Protocol
was	O
to	O
minimize	O
optional	O
features	O
.	O
</s>
<s>
However	O
,	O
XML	B-Protocol
's	O
well-formedness	O
rules	O
cannot	O
support	O
Wiki-like	O
languages	O
,	O
leaving	O
them	O
unstandardized	O
and	O
difficult	O
to	O
integrate	O
with	O
non-text	O
information	O
systems	O
.	O
</s>
<s>
The	O
usual	O
(	O
default	O
)	O
SGML	B-Language
concrete	O
syntax	O
resembles	O
this	O
example	O
,	O
which	O
is	O
the	O
default	O
HTML	B-Language
concrete	O
syntax	O
:	O
</s>
<s>
SGML	B-Language
provides	O
an	O
abstract	O
syntax	O
that	O
can	O
be	O
implemented	O
in	O
many	O
different	O
types	O
of	O
concrete	O
syntax	O
.	O
</s>
<s>
Although	O
the	O
markup	O
norm	O
is	O
using	O
angle	O
brackets	O
as	O
start	O
-	O
and	O
end-tag	O
delimiters	B-Algorithm
in	O
an	O
SGML	B-Language
document	O
(	O
per	O
the	O
standard-defined	O
reference	O
concrete	O
syntax	O
)	O
,	O
it	O
is	O
possible	O
to	O
use	O
other	O
characters	O
—	O
provided	O
a	O
suitable	O
concrete	O
syntax	O
is	O
defined	O
in	O
the	O
document	O
's	O
SGML	B-Language
declaration	O
.	O
</s>
<s>
For	O
example	O
,	O
an	O
SGML	B-Language
interpreter	O
might	O
be	O
programmed	O
to	O
parse	B-Language
GML	B-Application
,	O
wherein	O
the	O
tags	O
are	O
delimited	B-Algorithm
with	O
a	O
left	O
colon	O
and	O
a	O
right	O
full	O
stop	O
,	O
and	O
an	O
:e	O
prefix	O
denotes	O
an	O
end	O
tag	O
:	O
:xmp.Hello	O
,	O
exmp	O
..	O
</s>
<s>
SGML	B-Language
has	O
features	O
for	O
reducing	O
the	O
number	O
of	O
characters	O
required	O
to	O
mark	O
up	O
a	O
document	O
,	O
which	O
must	O
be	O
enabled	O
in	O
the	O
SGML	B-Language
Declaration	O
.	O
</s>
<s>
SGML	B-Language
processors	O
need	O
not	O
support	O
every	O
available	O
feature	O
,	O
thus	O
allowing	O
applications	O
to	O
tolerate	O
many	O
types	O
of	O
inadvertent	O
markup	O
omissions	O
;	O
however	O
,	O
SGML	B-Language
systems	O
usually	O
are	O
intolerant	O
of	O
invalid	O
structures	O
.	O
</s>
<s>
XML	B-Protocol
is	O
intolerant	O
of	O
syntax	O
omissions	O
,	O
and	O
does	O
not	O
require	O
a	O
DTD	O
for	O
checking	O
well-formedness	O
.	O
</s>
<s>
the	O
OMITTAG	O
feature	O
is	O
enabled	O
in	O
the	O
SGML	B-Language
Declaration	O
,	O
</s>
<s>
For	O
example	O
,	O
if	O
OMITTAG	O
YES	O
is	O
specified	O
in	O
the	O
SGML	B-Language
Declaration	O
(	O
enabling	O
the	O
OMITTAG	O
feature	O
)	O
,	O
and	O
the	O
DTD	O
includes	O
the	O
following	O
declarations	O
:	O
</s>
<s>
This	O
is	O
syntactically	O
different	O
from	O
XML	B-Protocol
empty	O
elements	O
in	O
this	O
regard	O
.	O
</s>
<s>
Tags	O
can	O
be	O
replaced	O
with	O
delimiter	B-Algorithm
strings	O
,	O
for	O
a	O
terser	O
markup	O
,	O
via	O
the	O
SHORTREF	O
feature	O
.	O
</s>
<s>
This	O
markup	O
style	O
is	O
now	O
associated	O
with	O
wiki	B-Protocol
markup	O
,	O
e.g.	O
</s>
<s>
SGML	B-Language
markup	O
languages	O
whose	O
concrete	O
syntax	O
enables	O
the	O
SHORTTAG	O
VALUE	O
feature	O
,	O
do	O
not	O
require	O
attribute	O
values	O
containing	O
only	O
alphanumeric	O
characters	O
to	O
be	O
enclosed	O
within	O
quotation	O
marks	O
—	O
either	O
double	O
"	O
"	O
(	O
LIT	O
)	O
or	O
single	O
'	O
'	O
(	O
LITA	O
)	O
—	O
so	O
that	O
the	O
previous	O
markup	O
example	O
could	O
be	O
written	O
:	O
</s>
<s>
One	O
feature	O
of	O
SGML	B-Language
markup	O
languages	O
is	O
the	O
"	O
presumptuous	O
empty	O
tagging	O
"	O
,	O
such	O
that	O
the	O
empty	O
end	O
tag	O
</> in <ITALICS>this</> "inherits" its value from the nearest previous full start tag, which, in this example, is <ITALICS>	O
(	O
in	O
other	O
words	O
,	O
it	O
closes	O
the	O
most	O
recently	O
opened	O
item	O
)	O
.	O
</s>
<s>
NOTE	O
:	O
XML	B-Protocol
defines	O
NESTC	O
with	O
a	O
/	O
,	O
and	O
NET	O
with	O
an	O
>	O
(	O
angled	O
bracket	O
)	O
—	O
hence	O
the	O
corresponding	O
construct	O
in	O
XML	B-Protocol
appears	O
as	O
.	O
</s>
<s>
(	O
and	O
"	O
#RE	O
;	O
#RS	O
;	O
"	O
is	O
a	O
short-reference	O
delimiter	B-Algorithm
in	O
the	O
concrete	O
syntax	O
)	O
,	O
then	O
:	O
</s>
<s>
SGML	B-Language
has	O
many	O
features	O
that	O
defied	O
convenient	O
description	O
with	O
the	O
popular	O
formal	O
automata	B-Application
theory	I-Application
and	O
the	O
contemporary	O
parser	B-Language
technology	O
of	O
the	O
1980s	O
and	O
the	O
1990s	O
.	O
</s>
<s>
A	O
report	O
on	O
an	O
early	O
implementation	O
of	O
a	O
parser	B-Language
for	O
basic	O
SGML	B-Language
,	O
the	O
Amsterdam	O
SGML	B-Language
Parser	B-Language
,	O
notes	O
and	O
specifies	O
various	O
differences	O
.	O
</s>
<s>
There	O
appears	O
to	O
be	O
no	O
definitive	O
classification	O
of	O
full	O
SGML	B-Language
against	O
a	O
known	O
class	O
of	O
formal	O
grammar	O
.	O
</s>
<s>
XML	B-Protocol
is	O
described	O
as	O
being	O
generally	O
parsable	B-Language
like	O
a	O
two-level	B-Language
grammar	I-Language
for	O
non-validated	O
XML	B-Protocol
and	O
a	O
Conway-style	O
pipeline	O
of	O
coroutines	B-Architecture
(	O
lexer	B-Application
,	O
parser	B-Language
,	O
validator	O
)	O
for	O
valid	O
XML	B-Protocol
.	O
</s>
<s>
The	O
SGML	B-Language
productions	O
in	O
the	O
ISO	O
standard	O
are	O
reported	O
to	O
be	O
LL(3 )	O
or	O
LL(4 )	O
.	O
</s>
<s>
XML-class	O
subsets	O
are	O
reported	O
to	O
be	O
expressible	O
using	O
a	O
W-grammar	B-Application
.	O
</s>
<s>
According	O
to	O
one	O
paper	O
,	O
and	O
probably	O
considered	O
at	O
an	O
information	O
set	O
or	O
parse	B-Language
tree	O
level	O
rather	O
than	O
a	O
character	O
or	O
delimiter	B-Algorithm
level	O
:	O
</s>
<s>
The	O
SGML	B-Language
standard	O
does	O
not	O
define	O
SGML	B-Language
with	O
formal	O
data	O
structures	O
,	O
such	O
as	O
parse	B-Language
trees	O
;	O
however	O
,	O
an	O
SGML	B-Language
document	O
is	O
constructed	O
of	O
a	O
rooted	O
directed	O
acyclic	O
graph	O
(	O
RDAG	O
)	O
of	O
physical	O
storage	O
units	O
known	O
as	O
"	O
entities	B-Language
"	O
,	O
which	O
is	O
parsed	B-Language
into	O
a	O
RDAG	O
of	O
structural	O
units	O
known	O
as	O
"	O
elements	O
"	O
.	O
</s>
<s>
The	O
physical	O
graph	O
is	O
loosely	O
characterized	O
as	O
an	O
entity	O
tree	O
,	O
but	O
entities	B-Language
might	O
appear	O
multiple	O
times	O
.	O
</s>
<s>
The	O
results	O
of	O
parsing	B-Language
can	O
also	O
be	O
understood	O
as	O
a	O
data	O
tree	O
in	O
different	O
notations	O
;	O
where	O
the	O
document	O
is	O
the	O
root	O
node	O
,	O
and	O
entities	B-Language
in	O
other	O
notations	O
(	O
text	O
,	O
graphics	O
)	O
are	O
child	O
nodes	O
.	O
</s>
<s>
SGML	B-Language
provides	O
apparatus	O
for	O
linking	O
to	O
and	O
annotating	O
external	O
non-SGML	O
entities	O
.	O
</s>
<s>
The	O
SGML	B-Language
standard	O
describes	O
it	O
in	O
terms	O
of	O
maps	O
and	O
recognition	O
modes	O
(	O
s9.6.1	O
)	O
.	O
</s>
<s>
Also	O
,	O
each	O
element	O
can	O
have	O
an	O
associated	O
delimiter	B-Algorithm
map	O
(	O
and	O
short	O
reference	O
map	O
)	O
,	O
which	O
determines	O
which	O
characters	O
are	O
treated	O
as	O
delimiters	B-Algorithm
in	O
context	O
.	O
</s>
<s>
The	O
SGML	B-Language
standard	O
characterizes	O
parsing	B-Language
as	O
a	O
state	B-Architecture
machine	I-Architecture
switching	O
between	O
recognition	O
modes	O
.	O
</s>
<s>
During	O
parsing	B-Language
,	O
there	O
is	O
a	O
stack	O
of	O
maps	O
that	O
configure	O
the	O
scanner	B-Application
,	O
while	O
the	O
tokenizer	B-Application
relates	O
to	O
the	O
recognition	O
modes	O
.	O
</s>
<s>
Parsing	B-Language
involves	O
traversing	O
the	O
dynamically-retrieved	O
entity	O
graph	O
,	O
finding/implying	O
tags	O
and	O
the	O
element	O
structure	O
,	O
and	O
validating	O
those	O
tags	O
against	O
the	O
grammar	O
.	O
</s>
<s>
An	O
unusual	O
aspect	O
of	O
SGML	B-Language
is	O
that	O
the	O
grammar	O
(	O
DTD	O
)	O
is	O
used	O
both	O
passively	O
—	O
to	O
recognize	O
lexical	O
structures	O
,	O
and	O
actively	O
—	O
to	O
generate	O
missing	O
structures	O
and	O
tags	O
that	O
the	O
DTD	O
has	O
declared	O
optional	O
.	O
</s>
<s>
It	O
was	O
this	O
active	O
use	O
of	O
grammars	O
that	O
made	O
concrete	O
SGML	B-Language
parsing	B-Language
difficult	O
to	O
formally	O
characterize	O
.	O
</s>
<s>
SGML	B-Language
uses	O
the	O
term	O
validation	O
for	O
both	O
recognition	O
and	O
generation	O
.	O
</s>
<s>
XML	B-Protocol
does	O
not	O
use	O
the	O
grammar	O
(	O
DTD	O
)	O
to	O
change	O
delimiter	B-Algorithm
maps	O
or	O
to	O
inform	O
the	O
parse	B-Language
modes	O
,	O
and	O
does	O
not	O
allow	O
tag	B-Language
omission	I-Language
;	O
consequently	O
,	O
XML	B-Protocol
validation	O
of	O
elements	O
is	O
not	O
active	O
in	O
the	O
sense	O
that	O
SGML	B-Language
validation	O
is	O
active	O
.	O
</s>
<s>
SGML	B-Language
without	O
a	O
DTD	O
(	O
e.g.	O
</s>
<s>
simple	O
XML	B-Protocol
)	O
,	O
is	O
a	O
grammar	O
or	O
a	O
language	O
;	O
SGML	B-Language
with	O
a	O
DTD	O
is	O
a	O
metalanguage	O
.	O
</s>
<s>
SGML	B-Language
with	O
an	O
SGML	B-Language
declaration	O
is	O
,	O
perhaps	O
,	O
a	O
meta-metalanguage	O
,	O
since	O
it	O
is	O
a	O
metalanguage	O
whose	O
declaration	O
mechanism	O
is	O
a	O
metalanguage	O
.	O
</s>
<s>
SGML	B-Language
has	O
an	O
abstract	O
syntax	O
implemented	O
by	O
many	O
possible	O
concrete	O
syntaxes	O
;	O
however	O
,	O
this	O
is	O
not	O
the	O
same	O
usage	O
as	O
in	O
an	O
abstract	B-Data_Structure
syntax	I-Data_Structure
tree	I-Data_Structure
and	O
as	O
in	O
a	O
concrete	O
syntax	O
tree	O
.	O
</s>
<s>
In	O
the	O
SGML	B-Language
usage	O
,	O
a	O
concrete	O
syntax	O
is	O
a	O
set	O
of	O
specific	O
delimiters	B-Algorithm
,	O
while	O
the	O
abstract	O
syntax	O
is	O
the	O
set	O
of	O
names	O
for	O
the	O
delimiters	B-Algorithm
.	O
</s>
<s>
The	O
XML	B-Protocol
Infoset	O
corresponds	O
more	O
to	O
the	O
programming	O
language	O
notion	O
of	O
abstract	O
syntax	O
introduced	O
by	O
John	O
McCarthy	O
.	O
</s>
<s>
The	O
W3C	O
XML	B-Protocol
(	O
Extensible	B-Protocol
Markup	I-Protocol
Language	I-Protocol
)	O
is	O
a	O
profile	O
(	O
subset	O
)	O
of	O
SGML	B-Language
designed	O
to	O
ease	O
the	O
implementation	O
of	O
the	O
parser	B-Language
compared	O
to	O
a	O
full	O
SGML	B-Language
parser	B-Language
,	O
primarily	O
for	O
use	O
on	O
the	O
World	O
Wide	O
Web	O
.	O
</s>
<s>
In	O
addition	O
to	O
disabling	O
many	O
SGML	B-Language
options	O
present	O
in	O
the	O
reference	O
syntax	O
(	O
such	O
as	O
omitting	O
tags	O
and	O
nested	O
subdocuments	O
)	O
XML	B-Protocol
adds	O
a	O
number	O
of	O
additional	O
restrictions	O
on	O
the	O
kinds	O
of	O
SGML	B-Language
syntax	O
.	O
</s>
<s>
For	O
example	O
,	O
despite	O
enabling	O
SGML	B-Language
shortened	O
tag	O
forms	O
,	O
XML	B-Protocol
does	O
not	O
allow	O
unclosed	O
start	O
or	O
end	O
tags	O
.	O
</s>
<s>
XML	B-Protocol
currently	O
is	O
more	O
widely	O
used	O
than	O
full	O
SGML	B-Language
.	O
</s>
<s>
XML	B-Protocol
has	O
lightweight	O
internationalization	O
based	O
on	O
Unicode	O
.	O
</s>
<s>
Applications	O
of	O
XML	B-Protocol
include	O
XHTML	B-Language
,	O
XQuery	B-Language
,	O
XSLT	B-Application
,	O
XForms	B-Application
,	O
XPointer	B-General_Concept
,	O
JSP	B-Language
,	O
SVG	B-Application
,	O
RSS	O
,	O
Atom	B-Application
,	O
XML-RPC	B-Protocol
,	O
RDF/XML	O
,	O
and	O
SOAP	B-Protocol
.	O
</s>
<s>
While	O
HTML	B-Language
(	O
Hyper	B-Language
Text	I-Language
Markup	I-Language
Language	I-Language
)	O
was	O
developed	O
partially	O
independently	O
and	O
in	O
parallel	O
with	O
SGML	B-Language
,	O
its	O
creator	O
,	O
Tim	O
Berners-Lee	O
,	O
intended	O
it	O
to	O
be	O
an	O
application	O
of	O
SGML	B-Language
.	O
</s>
<s>
The	O
design	O
of	O
HTML	B-Language
was	O
therefore	O
inspired	O
by	O
SGML	B-Language
tagging	O
,	O
but	O
,	O
since	O
no	O
clear	O
expansion	O
and	O
parsing	B-Language
guidelines	O
were	O
established	O
,	O
most	O
actual	O
HTML	B-Language
documents	O
are	O
not	O
valid	O
SGML	B-Language
documents	O
.	O
</s>
<s>
Later	O
,	O
HTML	B-Language
was	O
reformulated	O
(	O
version	O
2.0	O
)	O
to	O
be	O
more	O
of	O
an	O
SGML	B-Language
application	O
;	O
however	O
,	O
the	O
HTML	B-Language
markup	O
language	O
has	O
many	O
legacy	O
-	O
and	O
exception-handling	O
features	O
that	O
differ	O
from	O
SGML	B-Language
's	O
requirements	O
.	O
</s>
<s>
HTML	B-Language
4	O
is	O
an	O
SGML	B-Language
application	O
that	O
fully	O
conforms	O
to	O
ISO	B-Language
8879	I-Language
–	O
SGML	B-Language
.	O
</s>
<s>
The	O
charter	O
for	O
the	O
2006	O
revival	O
of	O
the	O
World	O
Wide	O
Web	O
Consortium	O
HTML	B-Language
Working	O
Group	O
says	O
,	O
"	O
the	O
Group	O
will	O
not	O
assume	O
that	O
an	O
SGML	B-Language
parser	B-Language
is	O
used	O
for	O
'	O
classic	O
HTML	B-Language
 '	O
"	O
.	O
</s>
<s>
Although	O
HTML	B-Language
syntax	I-Language
closely	O
resembles	O
SGML	B-Language
syntax	O
with	O
the	O
default	O
reference	O
concrete	O
syntax	O
,	O
HTML5	B-Application
abandons	O
any	O
attempt	O
to	O
define	O
HTML	B-Language
as	O
an	O
SGML	B-Language
application	O
,	O
explicitly	O
defining	O
its	O
own	O
parsing	B-Language
rules	O
,	O
which	O
more	O
closely	O
match	O
existing	O
implementations	O
and	O
documents	O
.	O
</s>
<s>
It	O
does	O
,	O
however	O
,	O
define	O
an	O
alternative	O
XHTML	B-Language
serialization	O
,	O
which	O
conforms	O
to	O
XML	B-Protocol
and	O
therefore	O
to	O
SGML	B-Language
as	O
well	O
.	O
</s>
<s>
The	O
second	O
edition	O
of	O
the	B-Application
Oxford	I-Application
English	I-Application
Dictionary	I-Application
(	O
OED	B-Application
)	O
is	O
entirely	O
marked	O
up	O
with	O
an	O
SGML-based	O
markup	O
language	O
using	O
the	O
LEXX	B-Application
text	O
editor	O
.	O
</s>
<s>
The	O
third	O
edition	O
is	O
marked	O
up	O
as	O
XML	B-Protocol
.	O
</s>
<s>
Other	O
document	O
markup	O
languages	O
are	O
partly	O
related	O
to	O
SGML	B-Language
and	O
XML	B-Protocol
,	O
but	O
—	O
because	O
they	O
cannot	O
be	O
parsed	B-Language
or	O
validated	O
or	O
other-wise	O
processed	O
using	O
standard	O
SGML	B-Language
and	O
XML	B-Protocol
tools	O
—	O
they	O
are	O
not	O
considered	O
either	O
SGML	B-Language
or	O
XML	B-Protocol
languages	O
;	O
the	O
Z	O
Format	O
markup	O
language	O
for	O
typesetting	O
and	O
documentation	O
is	O
an	O
example	O
.	O
</s>
<s>
Several	O
modern	O
programming	O
languages	O
support	O
tags	O
as	O
primitive	O
token	O
types	O
,	O
or	O
now	O
support	O
Unicode	O
and	O
regular	B-Language
expression	I-Language
pattern-matching	O
.	O
</s>
<s>
An	O
example	O
is	O
the	O
Scala	B-Application
programming	I-Application
language	I-Application
.	O
</s>
<s>
Document	O
markup	O
languages	O
defined	O
using	O
SGML	B-Language
are	O
called	O
"	O
applications	O
"	O
by	O
the	O
standard	O
;	O
many	O
pre-XML	O
SGML	B-Language
applications	O
were	O
proprietary	O
property	O
of	O
the	O
organizations	O
which	O
developed	O
them	O
,	O
and	O
thus	O
unavailable	O
in	O
the	O
World	O
Wide	O
Web	O
.	O
</s>
<s>
The	O
following	O
list	O
is	O
of	O
pre-XML	O
SGML	B-Language
applications	O
.	O
</s>
<s>
Text	B-Language
Encoding	I-Language
Initiative	I-Language
(	O
TEI	O
)	O
is	O
an	O
academic	O
consortium	O
that	O
designs	O
,	O
maintains	O
,	O
and	O
develops	O
technical	O
standards	O
for	O
digital-format	O
textual	O
representation	O
applications	O
.	O
</s>
<s>
DocBook	B-Protocol
is	O
a	O
markup	O
language	O
originally	O
created	O
as	O
an	O
SGML	B-Language
application	O
,	O
designed	O
for	O
authoring	O
technical	O
documentation	O
;	O
DocBook	B-Protocol
currently	O
is	O
an	O
XML	B-Protocol
application	O
.	O
</s>
<s>
CALS	B-Language
(	O
Continuous	B-Language
Acquisition	I-Language
and	I-Language
Life-cycle	I-Language
Support	I-Language
)	O
is	O
a	O
US	O
Department	O
of	O
Defense	O
(	O
DoD	O
)	O
initiative	O
for	O
electronically	O
capturing	O
military	O
documents	O
and	O
for	O
linking	O
related	O
data	O
and	O
information	O
.	O
</s>
<s>
HyTime	B-Language
defines	O
a	O
set	O
of	O
hypertext-oriented	O
element	O
types	O
that	O
allow	O
SGML	B-Language
document	O
authors	O
to	O
build	O
hypertext	O
and	O
multimedia	O
presentations	O
.	O
</s>
<s>
LinuxDoc	B-Operating_System
.	O
</s>
<s>
Documentation	O
for	O
Linux	B-Application
packages	O
has	O
used	O
the	O
LinuxDoc	B-Operating_System
SGML	B-Language
DTD	O
and	O
Docbook	B-Protocol
XML	B-Language
DTD	I-Language
.	O
</s>
<s>
AAP	B-General_Concept
DTD	I-General_Concept
is	O
a	O
document	B-Language
type	I-Language
definition	I-Language
for	O
scientific	O
documents	O
,	O
defined	O
by	O
the	O
Association	O
of	O
American	O
Publishers	O
.	O
</s>
<s>
ISO	B-General_Concept
12083	I-General_Concept
,	O
a	O
successor	O
to	O
AAP	O
DTP	O
,	O
is	O
an	O
international	O
SGML	B-Language
standard	O
for	O
document	O
interchange	O
between	O
authors	O
and	O
publishers	O
.	O
</s>
<s>
SGMLguid	B-General_Concept
was	O
an	O
early	O
SGML	B-Language
document	B-Language
type	I-Language
definition	I-Language
created	O
,	O
developed	O
and	O
used	O
at	O
CERN	O
.	O
</s>
<s>
Significant	O
open-source	B-Application
implementations	O
of	O
SGML	B-Language
have	O
included	O
:	O
</s>
<s>
SP	O
and	O
Jade	O
,	O
the	O
associated	O
DSSSL	B-Language
processors	O
,	O
are	O
maintained	O
by	O
the	O
project	O
,	O
and	O
are	O
common	O
parts	O
of	O
Linux	B-Application
distributions	O
.	O
</s>
<s>
A	O
general	O
archive	O
of	O
SGML	B-Language
software	O
and	O
materials	O
resides	O
at	O
.	O
</s>
<s>
The	O
original	O
HTML	B-Language
parser	B-Language
class	O
,	O
in	O
Sun	O
System	O
's	O
implementation	O
of	O
Java	O
,	O
is	O
a	O
limited-features	O
SGML	B-Language
parser	B-Language
,	O
using	O
SGML	B-Language
terminology	O
and	O
concepts	O
.	O
</s>
