<s>
DocBook	B-Protocol
is	O
a	O
semantic	B-Application
markup	O
language	O
for	O
technical	O
documentation	O
.	O
</s>
<s>
As	O
a	O
semantic	B-Application
language	O
,	O
DocBook	B-Protocol
enables	O
its	O
users	O
to	O
create	O
document	O
content	O
in	O
a	O
presentation-neutral	O
form	O
that	O
captures	O
the	O
logical	O
structure	O
of	O
the	O
content	O
;	O
that	O
content	O
can	O
then	O
be	O
published	O
in	O
a	O
variety	O
of	O
formats	O
,	O
including	O
HTML	B-Language
,	O
XHTML	B-Language
,	O
EPUB	O
,	O
PDF	B-Application
,	O
man	B-Protocol
pages	I-Protocol
,	O
Web	O
help	O
and	O
HTML	B-Protocol
Help	I-Protocol
,	O
without	O
requiring	O
users	O
to	O
make	O
any	O
changes	O
to	O
the	O
source	O
.	O
</s>
<s>
In	O
other	O
words	O
,	O
when	O
a	O
document	O
is	O
written	O
in	O
DocBook	B-Protocol
format	O
it	O
becomes	O
easily	O
portable	O
into	O
other	O
formats	O
,	O
rather	O
than	O
needing	O
to	O
be	O
rewritten	O
.	O
</s>
<s>
DocBook	B-Protocol
is	O
an	O
XML	B-Protocol
language	O
.	O
</s>
<s>
In	O
its	O
current	O
version	O
(	O
5.x	O
)	O
,	O
DocBook	B-Protocol
's	O
language	O
is	O
formally	O
defined	O
by	O
a	O
RELAX	B-Language
NG	I-Language
schema	B-Language
with	O
integrated	O
Schematron	B-Language
rules	O
.	O
</s>
<s>
(	O
There	O
are	O
also	O
W3C	O
XML	O
Schema+Schematron	O
and	O
Document	B-Language
Type	I-Language
Definition	I-Language
(	O
DTD	B-Language
)	O
versions	O
of	O
the	O
schema	B-Language
available	O
,	O
but	O
these	O
are	O
considered	O
non-standard	O
.	O
)	O
</s>
<s>
As	O
a	O
semantic	B-Application
language	O
,	O
DocBook	B-Protocol
documents	O
do	O
not	O
describe	O
what	O
their	O
contents	O
"	O
look	O
like	O
"	O
,	O
but	O
rather	O
the	O
meaning	O
of	O
those	O
contents	O
.	O
</s>
<s>
For	O
example	O
,	O
rather	O
than	O
explaining	O
how	O
the	O
abstract	O
for	O
an	O
article	O
might	O
be	O
visually	O
formatted	O
,	O
DocBook	B-Protocol
simply	O
says	O
that	O
a	O
particular	O
section	O
is	O
an	O
abstract	O
.	O
</s>
<s>
DocBook	B-Protocol
provides	O
a	O
vast	O
number	O
of	O
semantic	B-Application
element	O
tags	O
.	O
</s>
<s>
DocBook	B-Protocol
's	O
structural	O
tags	O
include	O
,	O
but	O
are	O
not	O
limited	O
to	O
:	O
</s>
<s>
Structural	O
elements	O
are	O
the	O
only	O
permitted	O
top-level	O
elements	O
in	O
a	O
DocBook	B-Protocol
document	O
.	O
</s>
<s>
DocBook	B-Protocol
semantics	B-Application
are	O
entirely	O
neutral	O
to	O
these	O
kinds	O
of	O
language-based	O
concepts	O
.	O
</s>
<s>
(	O
The	O
DocBook	B-Protocol
specification	O
does	O
say	O
that	O
it	O
expects	O
different	O
typographical	O
treatment	O
,	O
but	O
it	O
does	O
not	O
offer	O
specific	O
requirements	O
as	O
to	O
what	O
this	O
treatment	O
may	O
be	O
.	O
)	O
</s>
<s>
That	O
is	O
,	O
a	O
DocBook	B-Protocol
processor	O
does	O
n't	O
have	O
to	O
transform	O
an	O
emphasis	O
tag	O
into	O
italics	O
.	O
</s>
<s>
A	O
reader-based	O
DocBook	B-Protocol
processor	O
could	O
increase	O
the	O
size	O
of	O
the	O
words	O
,	O
or	O
,	O
a	O
text-based	O
processor	O
could	O
use	O
bold	O
instead	O
of	O
italics	O
.	O
</s>
<s>
All	O
DocBook	B-Protocol
elements	O
are	O
in	O
an	O
XML	B-Language
Namespace	I-Language
,	O
so	O
the	O
root	O
element	O
has	O
an	O
xmlns	B-Language
attribute	O
to	O
set	O
the	O
current	O
namespace	O
.	O
</s>
<s>
Also	O
,	O
the	O
root	O
element	O
of	O
a	O
DocBook	B-Protocol
document	O
must	O
have	O
a	O
version	O
that	O
specifies	O
the	O
version	O
of	O
the	O
format	O
that	O
the	O
document	O
is	O
built	O
on	O
.	O
</s>
<s>
(	O
XML	B-Protocol
documents	I-Protocol
can	O
include	O
elements	O
from	O
multiple	O
namespaces	O
at	O
once	O
,	O
like	O
the	O
id	O
attributes	O
in	O
the	O
example	O
.	O
)	O
</s>
<s>
Rules	O
are	O
formally	O
defined	O
in	O
the	O
DocBook	B-Protocol
XML	B-Language
schema	I-Language
.	O
</s>
<s>
Appropriate	O
programming	O
tools	O
can	O
validate	O
an	O
XML	B-Protocol
document	I-Protocol
(	O
DocBook	B-Protocol
or	O
otherwise	O
)	O
,	O
against	O
its	O
corresponding	O
schema	B-Language
,	O
to	O
determine	O
if	O
(	O
and	O
where	O
)	O
the	O
document	O
fails	O
to	O
conform	O
to	O
that	O
schema	B-Language
.	O
</s>
<s>
XML	B-Protocol
editing	O
tools	O
can	O
also	O
use	O
schema	B-Language
information	O
to	O
avoid	O
creating	O
non-conforming	O
documents	O
in	O
the	O
first	O
place	O
.	O
</s>
<s>
Because	O
DocBook	B-Protocol
is	O
XML	B-Protocol
,	O
documents	O
can	O
be	O
created	O
and	O
edited	O
with	O
any	O
text	O
editor	O
.	O
</s>
<s>
A	O
dedicated	O
XML	B-Protocol
editor	I-Protocol
is	O
likewise	O
a	O
functional	O
DocBook	B-Protocol
editor	O
.	O
</s>
<s>
DocBook	B-Protocol
provides	O
schema	B-Language
files	I-Language
for	O
popular	O
XML	B-Language
schema	I-Language
languages	O
,	O
so	O
any	O
XML	B-Protocol
editor	I-Protocol
that	O
can	O
provide	O
content	O
completion	O
based	O
on	O
a	O
schema	B-Language
can	O
do	O
so	O
for	O
DocBook	B-Protocol
.	O
</s>
<s>
Many	O
graphical	O
or	O
WYSIWYG	B-Application
XML	B-Protocol
editors	I-Protocol
come	O
with	O
the	O
ability	O
to	O
edit	O
DocBook	B-Protocol
like	O
a	O
word	B-General_Concept
processor	I-General_Concept
.	O
</s>
<s>
Tables	O
,	O
list	O
items	O
,	O
and	O
other	O
stylized	O
content	O
can	O
be	O
copied	O
and	O
pasted	O
into	O
the	O
DocBook	B-Protocol
editor	O
and	O
will	O
be	O
preserved	O
in	O
the	O
DocBook	B-Protocol
XML	B-Protocol
output	O
.	O
</s>
<s>
Because	O
DocBook	B-Protocol
conforms	O
to	O
a	O
well-defined	O
XML	B-Language
schema	I-Language
,	O
documents	O
can	O
be	O
validated	O
and	O
processed	O
using	O
any	O
tool	O
or	O
programming	O
language	O
that	O
includes	O
XML	B-Protocol
support	O
.	O
</s>
<s>
DocBook	B-Protocol
began	O
in	O
1991	O
in	O
discussion	O
groups	O
on	O
Usenet	B-Application
and	O
eventually	O
became	O
a	O
joint	O
project	O
of	O
HAL	O
Computer	O
Systems	O
and	O
O'Reilly	O
&	O
Associates	O
and	O
eventually	O
spawned	O
its	O
own	O
maintenance	O
organization	O
(	O
the	O
Davenport	O
Group	O
)	O
before	O
moving	O
in	O
1998	O
to	O
the	O
SGML	B-Language
Open	O
consortium	O
,	O
which	O
subsequently	O
became	O
OASIS	O
.	O
</s>
<s>
DocBook	B-Protocol
is	O
currently	O
maintained	O
by	O
the	O
DocBook	B-Protocol
Technical	O
Committee	O
at	O
OASIS	O
.	O
</s>
<s>
DocBook	B-Protocol
is	O
available	O
in	O
both	O
SGML	B-Language
and	O
XML	B-Protocol
forms	O
,	O
as	O
a	O
DTD	B-Language
.	O
</s>
<s>
RELAX	B-Language
NG	I-Language
and	O
W3C	O
XML	B-Language
Schema	I-Language
forms	O
of	O
the	O
XML	B-Protocol
version	O
are	O
available	O
.	O
</s>
<s>
Starting	O
with	O
DocBook	B-Protocol
5	O
,	O
the	O
RELAX	B-Language
NG	I-Language
version	O
is	O
the	O
"	O
normative	O
"	O
form	O
from	O
which	O
the	O
other	O
formats	O
are	O
generated	O
.	O
</s>
<s>
DocBook	B-Protocol
originally	O
started	O
out	O
as	O
an	O
SGML	B-Language
application	O
,	O
but	O
an	O
equivalent	O
XML	B-Protocol
application	O
was	O
developed	O
and	O
has	O
now	O
replaced	O
the	O
SGML	B-Language
one	O
for	O
most	O
uses	O
.	O
</s>
<s>
(	O
Starting	O
with	O
version	O
4	O
of	O
the	O
SGML	B-Language
DTD	B-Language
,	O
the	O
XML	B-Language
DTD	I-Language
continued	O
with	O
this	O
version	O
numbering	O
scheme	O
.	O
)	O
</s>
<s>
Initially	O
,	O
a	O
key	O
group	O
of	O
software	O
companies	O
used	O
DocBook	B-Protocol
since	O
their	O
representatives	O
were	O
involved	O
in	O
its	O
initial	O
design	O
.	O
</s>
<s>
Eventually	O
,	O
however	O
,	O
DocBook	B-Protocol
was	O
adopted	O
by	O
the	O
open	O
source	O
community	O
where	O
it	O
has	O
become	O
a	O
standard	O
for	O
creating	O
documentation	O
for	O
many	O
projects	O
,	O
including	O
FreeBSD	B-Operating_System
,	O
KDE	B-Application
,	O
GNOME	B-Application
desktop	I-Application
documentation	O
,	O
the	O
GTK+	B-Application
API	B-Application
references	O
,	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
documentation	O
(	O
which	O
,	O
as	O
of	O
July	O
2016	O
,	O
is	O
transitioning	O
to	O
Sphinx/reStructuredText	O
)	O
,	O
and	O
the	O
work	O
of	O
the	O
Linux	B-Operating_System
Documentation	O
Project	O
.	O
</s>
<s>
Until	O
DocBook	B-Protocol
5	O
,	O
DocBook	B-Protocol
was	O
defined	O
normatively	O
by	O
a	O
Document	B-Language
Type	I-Language
Definition	I-Language
(	O
DTD	B-Language
)	O
.	O
</s>
<s>
Because	O
DocBook	B-Protocol
was	O
built	O
originally	O
as	O
an	O
application	O
of	O
SGML	B-Language
,	O
the	O
DTD	B-Language
was	O
the	O
only	O
available	O
schema	B-Language
language	O
.	O
</s>
<s>
DocBook	B-Protocol
4.x	O
formats	O
can	O
be	O
SGML	B-Language
or	O
XML	B-Protocol
,	O
but	O
the	O
XML	B-Protocol
version	O
does	O
not	O
have	O
its	O
own	O
namespace	O
.	O
</s>
<s>
DocBook	B-Protocol
4.x	O
formats	O
had	O
to	O
live	O
within	O
the	O
restrictions	O
of	O
being	O
defined	O
by	O
a	O
DTD	B-Language
.	O
</s>
<s>
That	O
is	O
,	O
an	O
element	O
named	O
info	O
must	O
contain	O
the	O
same	O
information	O
no	O
matter	O
where	O
it	O
is	O
in	O
the	O
DocBook	B-Protocol
file	O
.	O
</s>
<s>
As	O
such	O
,	O
there	O
are	O
many	O
kinds	O
of	O
info	O
elements	O
in	O
DocBook	B-Protocol
4.x	O
:	O
bookinfo	O
,	O
chapterinfo	O
,	O
etc	O
.	O
</s>
<s>
However	O
,	O
because	O
the	O
format	O
was	O
defined	O
by	O
a	O
DTD	B-Language
,	O
it	O
did	O
have	O
to	O
be	O
named	O
as	O
such	O
.	O
</s>
<s>
The	O
root	O
element	O
does	O
not	O
have	O
or	O
need	O
a	O
version	O
,	O
as	O
the	O
version	O
is	O
built	O
into	O
the	O
DTD	B-Language
declaration	O
at	O
the	O
top	O
of	O
a	O
pre-DocBook	O
5	O
document	O
.	O
</s>
<s>
DocBook	B-Protocol
4.x	O
documents	O
are	O
not	O
compatible	O
with	O
DocBook	B-Protocol
5	O
,	O
but	O
can	O
be	O
converted	O
into	O
DocBook	B-Protocol
5	O
documents	O
via	O
an	O
XSLT	B-Application
stylesheet	O
.	O
</s>
<s>
One	O
(	O
db4-upgrade.xsl	O
)	O
is	O
provided	O
as	O
part	O
of	O
the	O
distribution	O
of	O
the	O
DocBook	B-Protocol
5	O
schema	B-Language
and	O
specification	O
package	O
.	O
</s>
<s>
DocBook	B-Protocol
files	O
are	O
used	O
to	O
prepare	O
output	O
files	O
in	O
a	O
wide	O
variety	O
of	O
formats	O
.	O
</s>
<s>
Nearly	O
always	O
,	O
this	O
is	O
accomplished	O
using	O
DocBook	B-Language
XSL	I-Language
stylesheets	O
.	O
</s>
<s>
These	O
are	O
XSLT	B-Application
stylesheets	O
that	O
transform	O
DocBook	B-Protocol
documents	O
into	O
a	O
number	O
of	O
formats	O
(	O
HTML	B-Language
,	O
XSL-FO	B-Language
for	O
later	O
conversion	O
into	O
PDF	B-Application
,	O
etc	O
.	O
)	O
.	O
</s>
<s>
Users	O
can	O
write	O
their	O
own	O
customized	O
stylesheets	O
or	O
even	O
a	O
full-fledged	O
program	O
to	O
process	O
the	O
DocBook	B-Protocol
into	O
an	O
appropriate	O
output	O
format	O
as	O
their	O
needs	O
dictate	O
.	O
</s>
<s>
Norman	O
Walsh	O
and	O
the	O
DocBook	B-Protocol
Project	O
development	O
team	O
maintain	O
the	O
key	O
application	O
for	O
producing	O
output	O
from	O
DocBook	B-Protocol
source	O
documents	O
:	O
A	O
set	O
of	O
XSLT	B-Application
stylesheets	O
(	O
as	O
well	O
as	O
a	O
legacy	O
set	O
of	O
DSSSL	B-Language
stylesheets	O
)	O
that	O
can	O
generate	O
high-quality	O
HTML	B-Language
and	O
print	O
(	O
FO/PDF	O
)	O
output	O
,	O
as	O
well	O
as	O
output	O
in	O
other	O
formats	O
,	O
including	O
RTF	O
,	O
man	B-Protocol
pages	I-Protocol
and	O
HTML	B-Protocol
Help	I-Protocol
.	O
</s>
<s>
Web	O
help	O
is	O
a	O
chunked	O
HTML	B-Language
output	O
format	O
in	O
the	O
DocBook	B-Language
XSL	I-Language
stylesheets	O
that	O
was	O
introduced	O
in	O
version	O
1.76.1	O
.	O
</s>
<s>
The	O
documentation	O
for	O
web	O
help	O
also	O
provides	O
an	O
example	O
of	O
web	O
help	O
and	O
is	O
part	O
of	O
the	O
DocBook	B-Language
XSL	I-Language
distribution	O
.	O
</s>
<s>
Search	O
has	O
stemming	B-General_Concept
,	O
match	O
highlighting	O
,	O
explicit	O
page-scoring	O
,	O
and	O
the	O
standard	O
multilingual	O
tokenizer	O
.	O
</s>
<s>
The	O
search	O
and	O
TOC	O
are	O
in	O
a	O
pane	O
that	O
appears	O
as	O
a	O
frameset	B-General_Concept
,	O
but	O
is	O
actually	O
implemented	O
with	O
div	B-General_Concept
tags	I-General_Concept
and	O
cookies	O
(	O
so	O
that	O
it	O
is	O
progressive	O
)	O
.	O
</s>
<s>
DocBook	B-Protocol
offers	O
a	O
large	O
number	O
of	O
features	O
that	O
may	O
be	O
overwhelming	O
to	O
a	O
new	O
user	O
.	O
</s>
<s>
For	O
those	O
who	O
want	O
the	O
convenience	O
of	O
DocBook	B-Protocol
without	O
a	O
steep	O
learning	O
curve	O
,	O
Simplified	O
DocBook	B-Protocol
was	O
designed	O
.	O
</s>
<s>
It	O
is	O
a	O
small	O
subset	O
of	O
DocBook	B-Protocol
designed	O
for	O
single	O
documents	O
such	O
as	O
articles	O
or	O
white	O
papers	O
(	O
i.e.	O
,	O
"	O
books	O
"	O
are	O
not	O
supported	O
)	O
.	O
</s>
<s>
The	O
Simplified	O
DocBook	B-Protocol
DTD	B-Language
is	O
currently	O
at	O
version	O
1.1	O
.	O
</s>
<s>
Ingo	O
Schwarze	O
,	O
the	O
author	O
of	O
OpenBSD	B-Operating_System
's	O
mandoc	B-Application
,	O
considers	O
DocBook	B-Protocol
inferior	O
to	O
the	O
semantic	B-Application
mdoc	O
macro	O
for	O
man	B-Protocol
pages	I-Protocol
.	O
</s>
<s>
In	O
an	O
attempt	O
to	O
write	O
a	O
DocBook-to-mdoc	O
converter	O
(	O
previous	O
converters	O
like	O
docbook-to-man	O
does	O
not	O
cover	O
semantic	B-Application
elements	O
)	O
,	O
he	O
finds	O
the	O
semantic	B-Application
parts	O
"	O
bloated	O
,	O
redundant	O
,	O
and	O
incomplete	O
at	O
the	O
same	O
time	O
"	O
compared	O
to	O
elements	O
covered	O
in	O
mdoc	O
.	O
</s>
<s>
Moreover	O
,	O
Schwarze	O
finds	O
the	O
DocBook	B-Protocol
specification	O
not	O
specific	O
enough	O
about	O
the	O
use	O
of	O
tags	O
,	O
the	O
language	O
non-portable	O
across	O
versions	O
,	O
rough	O
in	O
details	O
and	O
overall	O
inconsistent	O
.	O
</s>
