<s>
The	O
STET	B-Application
text	B-Application
editor	I-Application
(	O
the	O
'	O
STructured	O
Editing	O
Tool	O
 '	O
)	O
may	O
have	O
been	O
the	O
first	O
folding	O
editor	O
;	O
its	O
first	O
version	O
was	O
written	O
in	O
1977	O
by	O
Mike	O
Cowlishaw	O
.	O
</s>
<s>
The	O
editor	O
runs	O
on	O
the	O
IBM	O
VM/CMS	B-Operating_System
operating	O
system	O
.	O
</s>
<s>
STET	B-Application
was	O
written	O
to	O
explore	O
an	O
approach	O
to	O
text	B-Application
editing	I-Application
that	O
followed	O
the	O
principles	O
of	O
Structured	B-Language
programming	I-Language
.	O
</s>
<s>
The	O
editor	O
,	O
like	O
many	O
text	B-Application
editors	I-Application
,	O
is	O
a	O
full-screen	O
editor	O
;	O
a	O
window	O
into	O
the	O
file	O
being	O
edited	O
is	O
displayed	O
and	O
the	O
lines	O
displayed	O
can	O
be	O
edited	O
directly	O
on-screen	O
by	O
insertions	O
,	O
deletions	O
,	O
or	O
overtyping	O
.	O
</s>
<s>
An	O
innovation	O
in	O
STET	B-Application
is	O
the	O
ability	O
to	O
mark	O
a	O
group	O
of	O
lines	O
using	O
the	O
<	O
line	O
command	O
to	O
mark	O
the	O
first	O
and	O
last	O
lines	O
of	O
a	O
group	O
.	O
</s>
<s>
The	O
structured	O
editing	O
facilities	O
of	O
STET	B-Application
are	O
based	O
on	O
the	O
concept	O
that	O
each	O
file	O
is	O
represented	O
as	O
a	O
collection	O
of	O
named	O
blocks	O
of	O
lines	O
.	O
</s>
<s>
The	O
block	O
reference	O
concept	O
is	O
very	O
similar	O
to	O
the	O
idea	O
of	O
links	O
in	O
a	O
Wikipedia	O
file	O
,	O
and	O
indeed	O
in	O
STET	B-Application
a	O
block	O
can	O
also	O
be	O
created	O
by	O
putting	O
a	O
new	O
reference	O
on	O
a	O
line	O
and	O
then	O
'	O
entering	O
 '	O
that	O
reference	O
to	O
edit	O
the	O
block	O
.	O
</s>
<s>
The	O
editor	O
is	O
written	O
in	O
PL/I	B-Language
except	O
for	O
the	O
3270	B-Operating_System
screen	O
interface	O
which	O
is	O
written	O
in	O
Assembler	O
.	O
</s>
<s>
STET	B-Application
was	O
written	O
and	O
maintained	O
by	O
Mike	O
Cowlishaw	O
from	O
1976	O
to	O
1979	O
and	O
then	O
taken	O
over	O
by	O
Steve	O
Davies	O
,	O
who	O
continued	O
to	O
enhance	O
and	O
maintain	O
it	O
through	O
the	O
1980s	O
.	O
</s>
<s>
Many	O
of	O
the	O
features	O
in	O
STET	B-Application
were	O
used	O
in	O
later	O
IBM	O
text	B-Application
editors	I-Application
,	O
including	O
XEDIT	B-Application
and	O
LEXX	O
.	O
</s>
