tt04

unix v7是最后一个广泛发布的研究型UNIX版本

.NH
Indents and Line Lengths
.PP
.UL troff
starts with a line length of 6.5 inches,
too wide for 8\(12\(mu11 paper.
To reset the line length,
use
the
.BD .ll
command, as in
.P1
^ll 6i
.P2
As with
.BD .sp ,
the actual length can be specified in several ways;
inches are probably the most intuitive.
.PP
The maximum line length provided by the typesetter is 7.5 inches, by the way.
To use the full width, you will have to reset the default physical left margin (``page offset''),
which is normally slightly less than one inch from the left edge
of the paper.
This is done by the
.BD .po
command.
.P1
^po 0
.P2
sets the offset as far to the left as it will go.
.WS
.PP
The indent command
.BD .in
causes the left margin to be indented
by some specified amount from the page offset.
If we use
.BD .in
to move the left margin in,
and
.BD .ll
to move the right margin to the left,
we can
make offset blocks of text:
.P1
^in 0.3i
^ll \(mi0.3i
text to be set into a block
^ll +0.3i
^in \(mi0.3i
.P2
will create a block that looks like this:
.P1
.fi
.ll -0.3i
Pater noster qui est in caelis sanctificetur nomen tuum;
adveniat regnum tuum; fiat voluntas tua, sicut in caelo,
et in terra. ...
Amen.
.ll +0.3i
.P2
Notice the use of `+' and `\(mi'
to specify the amount of change.
These change the previous setting by the specified amount,
rather than just overriding it.
The distinction is quite important:
.BD .ll\ +1i
makes lines one inch longer;
.BD .ll\ 1i
makes them one inch
.ul
long.
.PP
With 
.BD .in ,
.BD .ll
and
.BD .po ,
the previous value is used if no argument is specified.
.PP
To indent a single line, use the `temporary indent'
command
.BD .ti .
For example, all paragraphs in this memo
effectively begin with the command
.P1
^ti 3
.P2
Three of what?
The default unit for
.BD .ti ,
as for most horizontally oriented commands
.BD .ll , (
.BD .in ,
.BD .po ),
is ems;
an em is roughly the width of the letter `m'
in the current point size.
(Precisely, a em in size
.ul
p
is
.ul
p
points.)
Although inches are usually clearer than ems to people who don't set type
for a living,
ems have a place:
they are a measure of size that is proportional to the current point size.
If you want to make text that keeps its proportions
regardless of point size,
you should use ems for all dimensions.
Ems can be specified as scale factors directly,
as in
.BD .ti\ 2.5m .
.PP
Lines can also be indented negatively
if the indent is already positive:
.P1
^ti \(mi0.3i
.P2
causes the next line to be moved back three tenths of an inch.
Thus to make a decorative initial capital,
we indent the whole paragraph, then move the letter `P' back with
a
.BD .ti
command:
.P1
.ll -0.3i
.fi
.in +.3i
.ti -0.3i
\s36\v'2'P\v'-2'\s0ater noster qui est in caelis sanctificetur
nomen tuum;
adveniat regnum tuum;
'in -.3i
fiat voluntas tua,
sicut in caelo, et in terra. ...
Amen.
.ll +0.3i
.P2
Of course, there is also some trickery to make the `P'
bigger (just a `\es36P\es0'),
and to move it
down from its normal position
(see the section on local motions).