<s>
Markdown	O
is	O
a	O
lightweight	B-Protocol
markup	I-Protocol
language	I-Protocol
for	O
creating	O
formatted	O
text	O
using	O
a	O
plain-text	B-Application
editor	I-Application
.	O
</s>
<s>
Markdown	O
is	O
widely	O
used	O
in	O
blogging	O
,	O
instant	B-Application
messaging	I-Application
,	O
online	B-Application
forums	I-Application
,	O
collaborative	B-Application
software	I-Application
,	O
documentation	O
pages	O
,	O
and	O
readme	O
files	O
.	O
</s>
<s>
Markdown	O
was	O
inspired	O
by	O
pre-existing	O
conventions	O
for	O
marking	O
up	O
plain	O
text	O
in	O
email	O
and	O
usenet	B-Application
posts	O
,	O
such	O
as	O
the	O
earlier	O
markup	O
languages	O
setext	B-Language
(	O
c	O
.	O
1992	O
)	O
,	O
Textile	B-Language
(	O
c	O
.	O
2002	O
)	O
,	O
and	O
reStructuredText	B-Language
(	O
c	O
.	O
2002	O
)	O
.	O
</s>
<s>
In	O
2002	O
Aaron	O
Swartz	O
created	O
atx	B-Language
and	O
referred	O
to	O
it	O
as	O
“	O
the	O
true	O
structured	O
text	O
format	O
”	O
.	O
</s>
<s>
Swartz	O
and	O
Gruber	O
then	O
worked	O
together	O
to	O
create	O
the	O
Markdown	O
language	O
in	O
2004	O
,	O
with	O
the	O
goal	O
of	O
enabling	O
people	O
"	O
to	O
write	O
using	O
an	O
easy-to-read	O
and	O
easy-to-write	O
plain	O
text	O
format	O
,	O
optionally	O
convert	O
it	O
to	O
structurally	O
valid	O
XHTML	B-Language
(	O
or	O
HTML	B-Language
)	O
.	O
"	O
</s>
<s>
Its	O
key	O
design	O
goal	O
was	O
readability	O
,	O
that	O
the	O
language	O
be	O
readable	O
as-is	O
,	O
without	O
looking	O
like	O
it	O
has	O
been	O
marked	O
up	O
with	O
tags	B-General_Concept
or	O
formatting	O
instructions	O
,	O
unlike	O
text	O
formatted	O
with	O
‘	O
heavier’	O
markup	O
languages	O
,	O
such	O
as	O
Rich	O
Text	O
Format	O
(	O
RTF	O
)	O
,	O
HTML	B-Language
,	O
or	O
even	O
wikitext	O
(	O
each	O
of	O
which	O
have	O
obvious	O
in-line	O
tags	B-General_Concept
and	O
formatting	O
instructions	O
which	O
can	O
make	O
the	O
text	O
more	O
difficult	O
for	O
humans	O
to	O
read	O
)	O
.	O
</s>
<s>
Gruber	O
wrote	O
a	O
Perl	B-Language
script	O
,	O
,	O
which	O
converts	O
marked-up	O
text	O
input	O
to	O
valid	O
,	O
well-formed	O
XHTML	B-Language
or	O
HTML	B-Language
and	O
replaces	O
angle	O
brackets	O
(	O
,	O
)	O
and	O
ampersands	O
(	O
)	O
with	O
their	O
corresponding	O
character	B-General_Concept
entity	I-General_Concept
references	I-General_Concept
.	O
</s>
<s>
It	O
can	O
take	O
the	O
role	O
of	O
a	O
standalone	O
script	O
,	O
a	O
plugin	B-Application
for	O
Blosxom	B-Protocol
or	O
a	O
Movable	B-Protocol
Type	I-Protocol
,	O
or	O
of	O
a	O
text	O
filter	O
for	O
BBEdit	B-Operating_System
.	O
</s>
<s>
As	O
Markdown	O
's	O
popularity	O
grew	O
rapidly	O
,	O
many	O
Markdown	O
implementations	O
appeared	O
,	O
driven	O
mostly	O
by	O
the	O
need	O
for	O
additional	O
features	O
such	O
as	O
tables	O
,	O
footnotes	O
,	O
definition	O
lists	O
,	O
and	O
Markdown	O
inside	O
HTML	B-Language
blocks	O
.	O
</s>
<s>
The	O
behavior	O
of	O
some	O
of	O
these	O
diverged	O
from	O
the	O
reference	O
implementation	O
,	O
as	O
Markdown	O
was	O
only	O
characterised	O
by	O
an	O
informal	O
specification	O
and	O
a	O
Perl	B-Language
implementation	O
for	O
conversion	O
to	O
HTML	B-Language
.	O
</s>
<s>
Nonetheless	O
,	O
the	O
following	O
websites	O
and	O
projects	O
have	O
adopted	O
CommonMark	O
:	O
Discourse	B-Protocol
,	O
GitHub	B-Application
,	O
GitLab	B-Application
,	O
Reddit	B-Application
,	O
Qt	B-Language
,	O
Stack	O
Exchange	O
(	O
Stack	B-Error_Name
Overflow	I-Error_Name
)	O
,	O
and	O
Swift	B-Application
.	O
</s>
<s>
introduced	O
MIME	B-Protocol
type	O
.	O
</s>
<s>
discussed	O
and	O
registered	O
the	O
variants	O
MultiMarkdown	B-Language
,	O
GitHub	B-Application
Flavored	I-Application
Markdown	I-Application
(	O
GFM	O
)	O
,	O
Pandoc	B-Language
,	O
and	O
Markdown	O
Extra	O
among	O
others	O
.	O
</s>
<s>
Websites	O
like	O
Bitbucket	B-Protocol
,	O
Diaspora	O
,	O
GitHub	B-Application
,	O
OpenStreetMap	O
,	O
Reddit	B-Application
,	O
SourceForge	B-Application
,	O
and	O
Stack	O
Exchange	O
use	O
variants	O
of	O
Markdown	O
to	O
facilitate	O
discussion	O
between	O
users	O
.	O
</s>
<s>
Depending	O
on	O
implementation	O
,	O
basic	O
inline	O
HTML	B-General_Concept
tags	I-General_Concept
may	O
be	O
supported	O
.	O
</s>
<s>
GitHub	B-Application
had	O
been	O
using	O
its	O
own	O
variant	O
of	O
Markdown	O
since	O
as	O
early	O
as	O
2009	O
,	O
adding	O
support	O
for	O
additional	O
formatting	O
such	O
as	O
tables	O
and	O
nesting	O
block	O
content	O
inside	O
list	O
elements	O
,	O
as	O
well	O
as	O
GitHub-specific	O
features	O
such	O
as	O
auto-linking	O
references	O
to	O
commits	O
,	O
issues	O
,	O
usernames	O
,	O
etc	O
.	O
</s>
<s>
In	O
2017	O
,	O
GitHub	B-Application
released	O
a	O
formal	O
specification	O
of	O
its	O
GitHub	B-Application
Flavored	I-Application
Markdown	I-Application
(	O
GFM	O
)	O
that	O
is	O
based	O
on	O
CommonMark	O
.	O
</s>
<s>
GitHub	B-Application
also	O
changed	O
the	O
parser	O
used	O
on	O
their	O
sites	O
accordingly	O
,	O
which	O
required	O
that	O
some	O
documents	O
be	O
changed	O
.	O
</s>
<s>
Markdown	O
Extra	O
is	O
a	O
lightweight	B-Protocol
markup	I-Protocol
language	I-Protocol
based	O
on	O
Markdown	O
implemented	O
in	O
PHP	B-Application
(	O
originally	O
)	O
,	O
Python	B-Language
and	O
Ruby	B-Language
.	O
</s>
<s>
Markdown	O
Extra	O
is	O
supported	O
in	O
some	O
content	B-Protocol
management	I-Protocol
systems	I-Protocol
such	O
as	O
Drupal	B-Application
and	O
TYPO3	B-Protocol
.	O
</s>
<s>
It	O
is	O
implemented	O
in	O
Elm	B-Language
and	O
TypeScript	B-Language
and	O
adds	O
additional	O
syntax	O
elements	O
to	O
define	O
features	O
like	O
:	O
</s>
<s>
<p>Most inline <abbr title="Hypertext Markup Language">HTML</abbr>	O
tags	B-General_Concept
are	O
supported.	O
<	O
/p	O
>A	O
link	O
.	O
</s>
<s>
Most	O
inline	O
HTML	B-General_Concept
tags	I-General_Concept
are	O
supported	O
.	O
</s>
<s>
Implementations	O
of	O
Markdown	O
are	O
available	O
for	O
over	O
a	O
dozen	O
programming	O
languages	O
;	O
in	O
addition	O
,	O
many	O
applications	O
,	O
platforms	O
and	O
frameworks	B-Architecture
support	O
Markdown	O
.	O
</s>
<s>
For	O
example	O
,	O
Markdown	O
plugins	B-Application
exist	O
for	O
every	O
major	O
blogging	O
platform	O
.	O
</s>
<s>
While	O
Markdown	O
is	O
a	O
minimal	O
markup	O
language	O
and	O
is	O
read	O
and	O
edited	O
with	O
a	O
normal	O
text	B-Application
editor	I-Application
,	O
there	O
are	O
specially	O
designed	O
editors	O
that	O
preview	O
the	O
files	O
with	O
styles	O
,	O
which	O
are	O
available	O
for	O
all	O
major	O
platforms	O
.	O
</s>
<s>
Many	O
general-purpose	O
text	O
and	O
code	B-Application
editors	I-Application
have	O
syntax	O
highlighting	O
plugins	B-Application
for	O
Markdown	O
built	O
into	O
them	O
or	O
available	O
as	O
optional	O
download	O
.	O
</s>
<s>
Editors	O
may	O
feature	O
a	O
side-by-side	O
preview	O
window	O
or	O
render	O
the	O
code	O
directly	O
in	O
a	O
WYSIWYG	B-Application
fashion	O
.	O
</s>
<s>
Obsidian	B-Protocol
is	O
note-taking	O
software	O
based	O
on	O
Markdown	O
files	O
.	O
</s>
<s>
The	O
GNOME	B-Language
Evolution	I-Language
email	O
client	O
supports	O
composing	O
messages	O
in	O
Markdown	O
format	O
,	O
with	O
the	O
ability	O
to	O
send	O
and	O
render	O
emails	O
in	O
pure	O
Markdown	O
format	O
(	O
Content-Type	O
:	O
text/markdown	O
;	O
)	O
or	O
to	O
convert	O
Markdown	O
to	O
plaintext	O
or	O
HTML	B-Language
email	O
when	O
sending	O
.	O
</s>
<s>
The	O
Mozilla	B-Application
Thunderbird	I-Application
email	O
client	O
supports	O
Markdown	O
through	O
the	O
""	O
add-on	O
.	O
</s>
<s>
Kanboard	B-Application
uses	O
the	O
standard	O
Markdown	O
syntax	O
as	O
its	O
only	O
formatting	O
syntax	O
for	O
task	O
descriptions	O
.	O
</s>
<s>
Discourse	B-Protocol
uses	O
the	O
CommonMark	O
flavor	O
of	O
Markdown	O
in	O
the	O
forum	O
post	O
composer	O
.	O
</s>
<s>
Bugzilla	B-Application
uses	O
a	O
customized	O
version	O
of	O
Markdown	O
.	O
</s>
