m3

unix v7是最后一个广泛发布的研究型UNIX版本

prefacing them with \fB\e"\fR.
The newline at the end of a comment cannot be concealed.
A line beginning with \fB\e"\fR will appear as a blank line and
behave like \fB.sp|1\fR;
a comment can be on a line by itself by beginning the line with \fB.\e"\fR.
.mh
Local Horizontal and Vertical Motions, and the Width Function
.sc
Local Motions.
The functions \fB\ev\'\fIN\fB\|\'\fR and
\fB\eh\'\fIN\fB\|\'\fR
can be used for \fIlocal\fR vertical and horizontal motion respectively.
The distance \fIN\fR may be negative; the \fIpositive\fR directions
are \fIrightward\fR and \fIdownward\fR.
A \fIlocal\fR motion is one contained \fIwithin\fR a line.
To avoid unexpected vertical dislocations, it is necessary that
the \fInet\fR vertical local motion within a word in filled text
and otherwise within a line balance to zero.
The above and certain other escape sequences providing local motion are
summarized in the following table.
.tr ||
.ds X \0\0\0
.TS
center box;
c2|cs2||c2|cs2
c1|c2c2||c2|c2c2.
Vertical	Effect in	Horizontal	Effect in
Local Motion	\*(TR	\*(NR	Local Motion	\*(TR	\*(NR
_
.sp.4
.TC
l2|ls2||l2|ls2.
\fB\*X\ev\'\fIN\|\^\fB\'\fR	Move distance \fIN\fR	\
\fB\*X\eh\'\fIN\|\^\fB\'\fR	Move distance \fIN\fR
.TC
_2|_2_2||l2|ls2.
x	x	x	\fB\*X\e\fR(space)	Unpaddable space-size space
.TC
l2|l2|l2||l2|ls2.
\fB\*X\eu\fR	\(12 em up	\(12 line up	\fB\*X\e0\fR	Digit-size space
.TC
l2|l2|l2||_2|_2_2.
\fB\*X\ed\fR	\(12 em down	\(12 line down	x	x	x
.TC
l2|l2|l2||l2|l2|l2.
\fB\*X\er\fR	1 em up	1 line up	\fB\*X\e\||\fR	1\(sl6 em space	ignored
			\fB\*X\e^\fR	1\(sl12 em space	ignored
.sp.4
.TE
.rm X
.tr |
As an example,
\fBE\s-2\v'-.4m'2\v'.4m'\s+2\fR
could be generated by the sequence
\fBE\es\-2\ev\'\-0.4m\'2\ev\'0.4m\'\es+2\fR;
it should be noted in this example that
the 0.4|em vertical motions are at the smaller size.
.sc
Width Function.
The \fIwidth\fR function \fB\ew\'\fIstring\fB\|\'\fR
generates the numerical width of \fIstring\fR (in basic units).
Size and font changes may be safely imbedded in \fIstring\fR,
and will not affect the current environment.
For example,
\&\fB.ti|\-\\w\'1.|\'u\fR could be used to
temporarily indent leftward a distance equal to the
size of the string "\fB1.|\fR".
.pg
The width function also sets three number registers.
The registers \fBst\fR and \fBsb\fR are set respectively to the highest and
lowest extent of \fIstring\fR relative to the baseline;
then, for example,
the total \fIheight\fR of the string is \fB\en(stu\-\en(sbu\fR.
In \*(TR the number register \fBct\fR is set to a value
between 0|and|3:
0 means that all of the characters in \fIstring\fR were short lower
case characters without descenders (like \fBe\fR);
1 means that at least one character has a descender (like \fBy\fR);
2 means that at least one character is tall (like \fBH\fR);
and 3 means that both tall characters and characters with
descenders are present.
.sc
Mark horizontal place.
The escape sequence \fB\ek\fIx\fR will cause the \fIcurrent\fR horizontal
position in the \fIinput line\fR to be stored in register \fIx\fR.
As an example,
the construction \fB\ekx\fIword\|\fB\eh\'\|~\|\enxu+2u\'\fIword\fB\fR
will embolden \fIword\fR by backing up to almost its beginning and overprinting it,
resulting in \kz\fIword\fR\h'|\nzu+2u'\fIword\fR.
.mh
Overstrike, Bracket, Line-drawing, and Zero-width Functions
.sc
Overstriking.
Automatically centered overstriking of up to nine characters
is provided by the \fIoverstrike\fR function
\fB\eo\'\fIstring\fB\|\'\fR.
The characters in \fIstring\fR overprinted with centers aligned; the total width
is that of the widest character.
\fIstring\fR should \fInot\fR contain local vertical motion.
As examples,
\fB\eo\'e\e\'\'\fR produces \fB\o'e\''\fR, and
\fB\eo\'\e(mo\e(sl\'\fR produces \fB\o'\(mo\(sl'\fR.
.sc
Zero-width characters.
The function \fB\ez\fIc\fR will output \fIc\fR without spacing over
it, and can be used to produce left-aligned overstruck
combinations.
As examples,
\fB\ez\e(ci\e(pl\fR will produce \fB\z\(ci\(pl\fR, and
\fB\e(br\ez\e(rn\e(ul\e(br\fR will produce the smallest possible
constructed box \fB\(br\z\(rn\(ul\(br\fR\|.
.sc
Large Brackets.
The Special Mathematical Font contains a number of bracket construction pieces
(\|\|\(lt\|\|\(lb\|\|\(rt\|\|\(rb\|\|\(lk\|\|\(rk\|\|\(bv\|\|\(lf\|\|\(rf\|\|\(lc\|\|\(rc\|\|)
that can be combined into various bracket styles.
The function \fB\eb\'\fIstring\fB\|\'\fR may be used to pile
up vertically the characters in \fIstring\fR
(the first character on top and the last at the bottom);
the characters are vertically separated by 1|em and the total
pile is centered 1\(sl2\|em above the current baseline
(\(12 line in \*(NR).
For example,
\fB\eb\'\|\e(lc\e(lf\|\'E\e\|~\|\eb\'\|\e(rc\e(rf\|\'\|\ex\'\|\-0.5m\'\|\ex\'0.5m\'\|\fR
produces
\x'-.5m'\x'.5m'\fB\b'\(lc\(lf'E\|\b'\(rc\(rf'\fR.
.sc
Line drawing.
.tr &&
The function \fB\e\|l\|\'\fINc\fB\|\'\fR will draw a string of repeated \fIc\fR\|'s towards the right for a distance \fIN\fR.
(\|\fB\el\fR is \fB\e\fR(lower case L).
If \fIc\fR looks like a continuation of
an expression for \fIN\fR, it may insulated from \fIN\fR with a \fB\e&\fR.
If \fIc\fR is not specified, the \fB\(ru\fR (baseline rule) is used
(underline character in \*(NR).
If \fIN\fR is negative, a backward horizontal motion
of size \fIN\fR is made \fIbefore\fR drawing the string.
Any space resulting from \fIN\fR\|\(sl(size of \fIc\fR) having a remainder is put at the beginning (left end)
of the string.
In the case of characters
that are designed to be connected such as
baseline-rule\ \fB\(ru\fR\|,
underrule\ \fB\(ul\fR\|,
and
root-en\ \fB\(rn\fR\|,
the remainder space is covered by over-lapping.
If \fIN\fR is \fIless\fR than the width of \fIc\fR,
a single \fIc\fR is centered on a distance \fIN\fR.
As an example, a macro to underscore a string can be written
.br
.tr &.
.x1
.ftB
.ne 2.1
&de us
\e\e$1\e\|l\|\'\|~\|0\e(ul\'
&&
.ftR
.x2
.ne2.1
.de xu
\\$1\l'|0\(ul'
..
or one to draw a box around a string
.x1
.ftB
&de bx
\e(br\e\|~\|\e\e$1\e\|~\|\e(br\e\|l\|\'\|~\|0\e(rn\'\e\|l\|\'\|~\|0\e(ul\'
&&
.ftR
.x2
.de bx
\(br\|\\$1\|\(br\l'|0\(rn'\l'|0\(ul'
..
such that
.x1
.ftB
&ul "underlined words"
.ftR
.x2
and
.x1
.ftB
&bx "words in a box"
.ftR
.x2
yield
.xu "underlined words"
and
.bx "words in a box"
\h'-\w'.'u'.
.pg
The function \fB\eL\'\|\fINc\fB\|\'\fR will draw a vertical line consisting
of the (optional) character \fIc\fR stacked vertically apart 1\|em
(1 line in \*(NR),
with the first two characters overlapped,
if necessary, to form a continuous line.
The default character is the \fIbox rule\fR |\(br| (\fB\|\e(br\fR);
the other suitable character is the \fIbold vertical\fR \|\(bv\| (\fB\|\e(bv\fR).
The line is begun without any initial motion relative to the
current base line.
A positive \fIN\fR specifies a line drawn downward and
a negative \fIN\fR specifies a line drawn upward.
After the line is drawn \fIno\fR compensating
motions are made;
the instantaneous baseline is at the \fIend\fR of the line.
.pg
.de eb
.sp -1
.nf
\h'-.5n'\L'|\\nzu-1'\l'\\n(.lu+1n\(ul'\L'-|\\nzu+1'\l'|0u-.5n\(ul'
.fi
..
.ne 2i
.mk z
The horizontal and vertical line drawing functions may be used
in combination to produce large boxes.
The zero-width \fIbox-rule\fR and the \(12-em wide \fIunderrule\fR
were \fIdesigned\fR to form corners when using 1-em vertical
spacings.
For example the macro
.x1
.ftB
\&.de eb
\&.sp \-1	\e"compensate for next automatic base-line spacing
\&.nf	\e"avoid possibly overflowing word buffer
.tr ||
\&\eh\'\-.5n\'\eL\'\||\|\e\enau\-1\'\el\'\e\en(.lu+1n\e(ul\'\eL\'\-\||\|\e\enau+1\'\el\'\||\|0u\-.5n\e(ul\'    \e"draw box
.tr |
.lg0
\&.fi
.lg
\&..
.ftR
.x2
will draw a box around some text whose beginning vertical place was
saved in number register \fIa\fR
(e. g. using \fB.mk|a\fR)
as done for this paragraph.
.eb