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.\"	@(#)m2	8.1 (Berkeley) 8/14/93
.\"
.\" $FreeBSD$
.tr |
.rm mx
.br
.mh
Line Length and Indenting
.pg
The maximum line length for fill mode may be set with \fBll\fR.
The indent may be set with \fBin\fR;
an indent applicable to \fIonly\fR the \fInext\fR output line may be set with \fBti\fR.
The line length includes indent space but \fInot\fR
page offset space.
The line-length minus the indent is the basis for centering with \fBce\fR.
The effect of \fBll\fR, \fBin\fR, or \fBti\fR
is delayed, if a partially collected line exists,
until after that line is output.
In fill mode the length of text on an output line is less than or equal to
the line length minus the indent.
The current line length and indent are available in registers \fB.l\fR and \fB.i\fR respectively.
The length of \fIthree-part titles\fR produced by \fBtl\fR
(see \(sc14) is \fIindependently\fR set by \fBlt\fR.
.h1
.bt
\fB&ll\fI|\(+-N\fR	6.5\|in	previous	E,\fBm\fR	Line length is set to \(+-\fIN\fR.
In \*(TR the maximum (line-length)+(page-offset) is about 7.54 inches.
.bt
\fB&in\fI|\(+-N\fR	\fIN\(eq\^\fR0	previous	B,E,\fBm\fR	Indent is set to \fI\(+-N\fR.
The indent is prepended to each output line.
.bt
\fB&ti\fI|\(+-N\fR	-	ignored	B,E,\fBm\fR	Temporary indent.
The \fInext\fR output text line will be indented a distance \fI\(+-N\fR
with respect to the current indent.
The resulting total indent may not be negative.
The current indent is not changed.
.mh
Macros, Strings, Diversion, and Position Traps
.sc
Macros and strings.
A \fImacro\fR is a named set of arbitrary \fIlines\fR that may be invoked by name or
with a \fItrap\fR.
A \fIstring\fR is a named string of \fIcharacters\fR,
\fInot\fR including a newline character,
that may be interpolated by name at any point.
Request, macro, and string names share the \fIsame\fR name list.
Macro and string names
may be one or two characters long and may usurp previously defined
request, macro, or string names.
Any of these entities may be renamed with \fBrn\fR
or removed with \fBrm\fR.
Macros are created by \fBde\fR and \fBdi\fR, and appended to by \fBam\fR and \fBda\fR;
\fBdi\fR and \fBda\fR cause normal output to be stored in a macro.
Strings are created by \fBds\fR and appended to by \fBas\fR.
A macro is invoked in the same way as a request;
a control line beginning \fB.\fIxx\fR will interpolate the contents of macro \fIxx\fR.
The remainder of the line may contain up to nine \fIarguments\fR.
The strings \fIx\fR and \fIxx\fR are interpolated at any desired point with
\fB\e\(**\fIx\fR and \fB\e\(**(\fIxx\fR respectively.
String references and macro invocations may be nested.
.sc
Copy mode input interpretation.
During the definition and extension
of strings and macros (not by diversion)
the input is read in \fIcopy mode\fR.
The input is copied without interpretation
\fIexcept\fR that:
.x1
.ds + \v'-.1m'\s-4\(bu\s+4\v'+.1m'
\(bu The contents of number registers indicated by \fB\en\fR are interpolated.
\(bu Strings indicated by \fB\e\(**\fR are interpolated.
\(bu Arguments indicated by \fB\e$\fR are interpolated.
\(bu Concealed newlines indicated by \fB\e\fR(newline) are eliminated.
\(bu Comments indicated by \fB\e"\fR are eliminated.
\(bu \fB\et\fR and \fB\ea\fR are interpreted as \s-1ASCII\s+1 horizontal tab and \s-1SOH\s+1 respectively (\(sc9).
\(bu \fB\e\e\fR is interpreted as \fB\e\fR.
\(bu \fB\e.\fR is interpreted as "\fB.\fR".
.x2
These interpretations can be suppressed by
prepending
a \fB\e\fR.
For example, since \fB\e\e\fR maps into a \fB\e\fR, \fB\e\en\fR will copy as \fB\en\fR which
will be interpreted as a number register indicator when the
macro or string is reread.
.sc
Arguments.
When a macro is invoked by name, the remainder of the line is
taken to contain up to nine arguments.
The argument separator is the space character, and arguments
may be surrounded by double-quotes to permit imbedded space characters.
Pairs of double-quotes may be imbedded in double-quoted arguments to
represent a single double-quote.
If the desired arguments won't fit on a line,
a concealed newline may be used to continue on the next line.
.pg
When a macro is invoked the \fIinput level\fR is \fIpushed down\fR and
any arguments available at the previous level become unavailable
until the macro is completely read and the previous level is restored.
A macro's own arguments can be interpolated at \fIany\fR point
within the macro with \fB\e$\fIN\fR, which interpolates the \fIN\fR\^th
argument
(1\(<=\fIN\fR\^\(<=9).
If an invoked argument doesn't exist,
a null string results.
For example, the macro \fIxx\fR may be defined by
.x1
.ft B
.ta .75i
&de xx	\e"begin definition
Today is \e\e$1 the \e\e$2.
&.	\e"end definition
.ft R
.x2
and called by
.x1
.ft B
&xx Monday 14th
.ft R
.x2
to produce the text
.x1
.ft B
Today is Monday the 14th.
.ft R
.x2
Note that the \fB\e$\fR
was concealed in the definition with a prepended \fB\e\fR.
The number of currently available
arguments is in the \fB.$\fR register.
.pg
No arguments are available at the top (non-macro) level
in this implementation.
Because string referencing is implemented
as an input-level push down,
no arguments are available from \fIwithin\fR a string.
No arguments are available within a trap-invoked macro.
.pg
Arguments are copied in \fIcopy mode\fR onto a stack
where they are available for reference.
The mechanism does not allow an argument to contain
a direct reference to a \fIlong\fR string
(interpolated at copy time) and it is advisable to
conceal string references (with an extra \fB\e\fR\|)
to delay interpolation until argument reference time.
.sc
Diversions.
Processed output may be diverted into a macro for purposes
such as footnote processing (see Tutorial \(scT5)
or determining the horizontal and vertical size of some text for
conditional changing of pages or columns.
A single diversion trap may be set at a specified vertical position.
The number registers \fBdn\fR and \fBdl\fR respectively contain the
vertical and horizontal size of the most
recently ended diversion.
Processed text that is diverted into a macro
retains the vertical size of each of its lines when reread
in \fInofill\fR mode
regardless of the current \fIV\fR.
Constant-spaced (\fBcs\fR) or emboldened (\fBbd\fR) text that is diverted
can be reread correctly only if these modes are again or still in effect
at reread time.
One way to do this is to imbed in the diversion the appropriate
\fBcs\fR or \fBbd\fR requests with the \fItransparent\fR
mechanism described in \(sc10.6.
.pg
Diversions may be nested
and certain parameters and registers
are associated
with the current diversion level
(the top non-diversion level may be thought of as the
0th diversion level).
These are the diversion trap and associated macro,
no-space mode,
the internally-saved marked place (see \fBmk\fR and \fBrt\fR),
the current vertical place (\fB.d\fR register),
the current high-water text base-line (\fB.h\fR register),
and the current diversion name (\fB.z\fR register).
.sc
Traps.
Three types of trap mechanisms are available\(empage traps, a diversion trap, and
an input-line-count trap.
Macro-invocation traps may be planted using \fBwh\fR at any page position including the top.
This trap position may be changed using \fBch\fR.
Trap positions at or below the bottom of the page
have no effect unless or until
moved to within the page or rendered effective by an increase in page length.
Two traps may be planted at the \fIsame\fR position only by first planting them at different
positions and then moving one of the traps;
the first planted trap will conceal the second unless and until the first one is moved
(see Tutorial Examples \(scT5).
If the first one is moved back, it again conceals the second trap.
The macro associated with a page trap is automatically
invoked when a line of text is output whose vertical size \fIreaches\fR
or \fIsweeps past\fR the trap position.
Reaching the bottom of a page springs the top-of-page trap, if any,
provided there is a next page.
The distance to the next trap position is available in the \fB.t\fR register;
if there are no traps between the current position and the bottom of the page,
the distance returned is the distance to the page bottom.
.pg
A macro-invocation trap effective in the current diversion may be planted using \fBdt\fR.
The \fB.t\fR register works in a diversion; if there is no subsequent trap a \fIlarge\fR
distance is returned.
For a description of input-line-count traps, see the \fBit\fR request below.
.h1
.bt
\fB&de\fI|xx|yy\fR	-	\fI.yy=\fB..\fR	-	Define or redefine the macro \fIxx\fR.
The contents of the macro begin on the next input line.
Input lines are copied in \fIcopy mode\fR until the definition is terminated by a
line beginning with \fB.\fIyy\fR,
whereupon the macro \fIyy\fR is called.
In the absence of \fIyy\fR, the definition
is terminated by a
line beginning with "\fB..\fR".
A macro may contain \fBde\fR requests
provided the terminating macros differ
or the contained definition terminator is concealed.
\&"\fB..\fR" can be concealed as
\fB\e\e..\fR which will copy as \fB\e..\fR and be reread as "\fB..\fR".
.bt
\fB&am\fI|xx|yy\fR	-	\fI.yy=\fB..\fR	-	Append to macro (append version of \fBde\fR).
.bt
\fB&ds\fI|xx|string\fR	-	ignored	-	Define a string
\fIxx\fR containing \fIstring\fR.
Any initial double-quote in \fIstring\fR is stripped off to permit
initial blanks.
.bt
\fB&as\fI|xx|string\fR	-	ignored	-	Append
\fIstring\fR to string \fIxx\fR
(append version of \fBds\fR).
.bt
\fB&rm\fI|xx\fR	-	ignored	-	Remove
request, macro, or string.
The name \fIxx\fR is removed from the name list and
any related storage space is freed.
Subsequent references will have no effect.
.bt
\fB&rn\fI|xx|yy\fR	-	ignored	-	Rename request, macro, or string
\fIxx\fR to \fIyy\fR.
If \fIyy\fR exists, it is first removed.
.bt
\fB&di|\fIxx\fR	-	end	D	Divert output to macro \fIxx\fR.
Normal text processing occurs during diversion
except that page offsetting is not done.
The diversion ends when the request \fBdi\fR or \fBda\fR is encountered without an argument;
extraneous
requests of this type should not appear when nested diversions are being used.
.bt
\fB&da|\fIxx\fR	-	end	D	Divert, appending to \fIxx\fR
(append version of \fBdi\fR).
.bt
\fB&wh\fI|N|xx\fR	-	-	\fBv\fR	Install
a trap to invoke \fIxx\fR at page position \fIN;\fR
a \fInegative N\fR will be interpreted with respect to the
page \fIbottom\fR.
Any macro previously planted at \fIN\fR is replaced by \fIxx\fR.
A zero \fIN\fR refers to the \fItop\fR of a page.
In the absence of \fIxx\fR, the first found trap at \fIN\fR, if any, is removed.
.bt
\fB&ch\fI|xx|N\fR	-	-	\fBv\fR	Change
the trap position for macro \fIxx\fR to be \fIN\fR.
In the absence of \fIN\fR, the trap, if any, is removed.
.bt
\fB&dt\fI|N|xx\fR	-	off	D,\fBv\fR	Install a diversion trap
at position \fIN\fR in the \fIcurrent\fR diversion to invoke
macro \fIxx\fR.
Another \fBdt\fR will redefine the diversion trap.
If no arguments are given, the diversion trap is removed.
.bt
\fB&it\fI|N|xx\fR	-	off	E	Set an input-line-count trap
to invoke the macro \fIxx\fR after \fIN\fR lines of \fItext\fR input
have been read
(control or request lines don't count).
The text may be in-line text or
text interpolated by inline or trap-invoked macros.
.bt
\fB&em\fI|xx\fR	none	none	-	The
macro \fIxx\fR will be invoked
when all input has ended.
The effect is the same as if the contents of \fIxx\fR had been at the end
of the last file processed.
.mh
Number Registers
.pg
A variety of parameters are available to the user as
predefined, named \fInumber registers\fR (see Summary and Index, page 7).
In addition, the user may define his own named registers.
Register names are one or two characters long and \fIdo not\fR conflict
with request, macro, or string names.
Except for certain predefined read-only registers,
a number register can be read, written, automatically
incremented or decremented, and interpolated
into the input in a variety of formats.
One common use of user-defined registers is to
automatically number sections, paragraphs, lines, etc.
A number register may be used any time numerical input is expected or desired
and may be used in numerical \fIexpressions\fR (\(sc1.4).
.pg
Number registers are created and modified using \fBnr\fR, which
specifies the name, numerical value, and the auto-increment size.
Registers are also modified, if accessed
with an auto-incrementing sequence.
If the registers \fIx\fR and \fIxx\fR both contain
\fIN\fR and have the auto-increment size \fIM\fR,
the following access sequences have the effect shown:
.TS
center box;
c2|c2|c
c2|c2|c
l2|c2|c
l2|c2|c
l2|l2|c.
	Effect on	Value
Sequence	Register	Interpolated
_
\fB\en\fIx\fR	none	\fIN\fR
\fB\en(\fIxx\fR	none	\fIN\fR
\fB\en+\fIx\fR	\fIx\fR incremented by \fIM\fR	\fIN+M\fR
\fB\en\-\fIx\fR	\fIx\fR decremented by \fIM\fR	\fIN\-M\fR
\fB\en+(\fIxx\fR	\fIxx\fR incremented by \fIM\fR	\fIN+M\fR
\fB\en\-(\fIxx\fR	\fIxx\fR decremented by \fIM\fR	\fIN\-M\fR
.TE
When interpolated, a number register is converted to
decimal (default),
decimal with leading zeros,
lower-case Roman,
upper-case Roman,
lower-case sequential alphabetic,
or
upper-case sequential alphabetic
according to the format specified by \fBaf\fR.
.h1
.bt
\fB&nr\fI|R|\(+-N|M\fR	-	-	\fBu\fR	\
The number register \fIR\fR is assigned the value \fI\(+-N\fR
with respect to the previous value, if any.
The increment for auto-incrementing is set to \fIM\fR.
.bt
\fB&af\fI|R|c\fR	arabic	-	-	Assign format \fIc\fR to register \fIR\fR.
The available formats are:
.TS
center box;
c2|c
c2|c
c2|l.
	Numbering
Format	Sequence
_
\fB1\fR	0,1,2,3,4,5,...
\fB001\fR	000,001,002,003,004,005,...
\fBi\fR	0,i,ii,iii,iv,v,...
\fBI\fR	0,I,II,III,IV,V,...
\fBa\fR	0,a,b,c,...,z,aa,ab,...,zz,aaa,...
\fBA\fR	0,A,B,C,...,Z,AA,AB,...,ZZ,AAA,...
.TE
An arabic format having \fIN\fR digits
specifies a field width of \fIN\fR digits (example 2 above).
The read-only registers and the \fIwidth\fR function (\(sc11.2)
are always arabic.
.bt
\fB&rr\fI|R\fR	-	ignored	-	Remove register \fIR\fR.
If many registers are being created dynamically, it
may become necessary to remove no longer used registers
to recapture internal storage space for newer registers.