'\" t
.TH @g@tbl @MAN1EXT@ "@MDATE@" "groff @VERSION@"
.SH Name
@g@tbl \- prepare tables for
.I groff
documents
.
.
.\" ====================================================================
.\" Legal Terms
.\" ====================================================================
.\"
.\" Copyright (C) 1989-2023 Free Software Foundation, Inc.
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of
.\" this manual under the conditions for verbatim copying, provided that
.\" the entire resulting derived work is distributed under the terms of
.\" a permission notice identical to this one.
.\"
.\" Permission is granted to copy and distribute translations of this
.\" manual into another language, under the above conditions for
.\" modified versions, except that this permission notice may be
.\" included in translations approved by the Free Software Foundation
.\" instead of in the original English.
.
.
.\" Save and disable compatibility mode (for, e.g., Solaris 10/11).
.do nr *groff_tbl_1_man_C \n[.cp]
.cp 0
.
.\" Define fallback for groff 1.23's MR macro if the system lacks it.
.nr do-fallback 0
.if !\n(.f           .nr do-fallback 1 \" mandoc
.if  \n(.g .if !d MR .nr do-fallback 1 \" older groff
.if !\n(.g           .nr do-fallback 1 \" non-groff *roff
.if \n[do-fallback]  \{\
.  de MR
.    ie \\n(.$=1 \
.      I \%\\$1
.    el \
.      IR \%\\$1 (\\$2)\\$3
.  .
.\}
.rr do-fallback
.
.
.\" ====================================================================
.SH Synopsis
.\" ====================================================================
.
.SY @g@tbl
.RB [ \-C ]
.RI [ file\~ .\|.\|.]
.YS
.
.
.SY @g@tbl
.B \-\-help
.YS
.
.
.SY @g@tbl
.B \-v
.
.SY @g@tbl
.B \-\-version
.YS
.
.
.\" ====================================================================
.SH Description
.\" ====================================================================
.
The GNU implementation of
.I tbl \" generic
is part of the
.MR groff @MAN1EXT@
document formatting system.
.
.I @g@tbl
is a
.MR @g@troff @MAN1EXT@
preprocessor that translates descriptions of tables embedded in
.MR roff @MAN7EXT@
input files into the language understood by
.IR @g@troff .
.
It copies the contents of each
.I file
to the standard output stream,
except that lines between
.B .TS
and
.B .TE
are interpreted as table descriptions.
.
While GNU
.IR tbl 's \" GNU
input syntax is highly compatible with AT&T
.IR tbl , \" AT&T
the output GNU
.I tbl \" GNU
produces cannot be processed by AT&T
.IR troff ; \" AT&T
GNU
.I troff \" GNU
(or a
.I troff \" generic
implementing any GNU extensions employed)
must be used.
.
Normally,
.I @g@tbl
is not executed directly by the user,
but invoked by specifying the
.B \-t
option to
.MR groff @MAN1EXT@ .
.
If no
.I file
operands are given on the command line,
or if
.I file
is
.RB \[lq] \- \[rq],
.I @g@tbl
reads the standard input stream.
.
.
.\" ====================================================================
.SS Overview
.\" ====================================================================
.
.I @g@tbl
expects to find table descriptions between input lines that begin with
.B .TS
(table start)
and
.B .TE
(table end).
.
Each such
.I table region
encloses one or more table descriptions.
.
Within a table region,
table descriptions beyond the first must each be preceded
by an input line beginning with
.BR .T& .
.
This mechanism does not start a new table region;
all table descriptions are treated as part of their
.BR .TS / .TE
enclosure,
even if they are boxed or have column headings that repeat on subsequent
pages
(see below).
.
.
.P
(Experienced
.I roff
users should observe that
.I @g@tbl
is not a
.I roff
language interpreter:
the default control character must be used,
and no spaces or tabs are permitted between the control character and
the macro name.
.
These
.I @g@tbl
input tokens remain as-is in the output,
where they become ordinary macro calls.
.
Macro packages often define
.BR TS ,
.BR T& ,
and
.B TE
macros to handle issues of table placement on the page.
.
.I @g@tbl
produces
.I groff
code to define these macros as empty if their definitions do not exist
when the formatter encounters a table region.)
.
.
.P
Each table region may begin with
.I region options,
and must contain one or more
.I table definitions;
each table definition contains a
.I format specification
followed by one or more input lines (rows) of
.I entries.
.
These entries comprise the
.I table data.
.
.
.
.\" ====================================================================
.SS "Region options"
.\" ====================================================================
.
The line immediately following the
.B .TS
token may specify region options,
keywords that influence the interpretation or rendering of the region as
a whole or all table entries within it indiscriminately.
.
They must be separated by commas,
spaces,
or tabs.
.
Those that require a parenthesized argument permit spaces and tabs
between the option's name and the opening parenthesis.
.
Options accumulate and cannot be unset within a region once declared;
if an option that takes a parameter is repeated,
the last occurrence controls.
.
If present,
the set of region options must be terminated with a semicolon
.RB ( ; ).
.
.
.P
Any of the
.BR allbox ,
.BR box ,
.BR doublebox ,
.BR frame ,
and
.B doubleframe
region options makes a table \[lq]boxed\[rq] for the purpose of later
discussion.
.
.
.TP
.B allbox
Enclose each table entry in a box;
implies
.BR box .
.
.
.TP
.B box
Enclose the entire table region in a box.
.
As a GNU extension,
the alternative option name
.B frame
is also recognized.
.
.
.TP
.B center
Center the table region with respect to the current indentation and line
length;
the default is to left-align it.
.
As a GNU extension,
the alternative option name
.B centre
is also recognized.
.
.
.TP
.BI decimalpoint( c )
Recognize character
.I c
as the decimal separator in columns using the
.B N
(numeric) classifier
(see subsection \[lq]Column classifiers\[rq] below).
.
This is a GNU extension.
.
.
.TP
.BI delim( xy )
Recognize characters
.I x
.RI and\~ y
as start and end delimiters,
respectively,
for
.MR @g@eqn @MAN1EXT@
input,
and ignore input between them.
.
.I x
.RI and\~ y
need not be distinct.
.
.
.TP
.B doublebox
Enclose the entire table region in a double box;
implies
.BR box .
.
As a GNU extension,
the alternative option name
.B \%doubleframe
is also recognized.
.
.
.TP
.B expand
Spread the table horizontally to fill the available space
(line length minus indentation)
by increasing column separation.
.
Ordinarily,
a table is made only as wide as necessary to accommodate the widths of
its entries and its column separations
(whether specified or default).
.
When
.B expand
applies to a table that exceeds the available horizontal space,
column separation is reduced as far as necessary
(even to zero).
.
.I @g@tbl
produces
.I groff
input that issues a diagnostic if such compression occurs.
.
The column modifier
.B x
(see below)
overrides this option.
.
.
.TP
.BI linesize( n )
Draw lines or rules
(e.g.,
from
.BR box )
with a thickness of
.IR n \~points.
.
The default is the current type size when the region begins.
.
This option is ignored on terminal devices.
.
.
.TP
.B nokeep
Don't use
.I roff
diversions to manage page breaks.
.
Normally,
.I @g@tbl
employs them to avoid breaking a page within a table row.
.
This usage can sometimes interact badly with macro packages' own use of
diversions\[em]when footnotes,
for example,
are employed.
.
This is a GNU extension.
.
.
.TP
.B nospaces
Ignore leading and trailing spaces in table entries.
.
This is a GNU extension.
.
.
.TP
.B nowarn
Suppress diagnostic messages produced at document formatting time when
the line or page lengths are inadequate to contain a table row.
.
This is a GNU extension.
.
.
.\" TODO: How about "right"?  (and "left" for symmetry)
.TP
.BI tab( c )
Use the character
.I c
instead of a tab to separate entries in a row of table data.
.
.
.\" ====================================================================
.SS "Table format specification"
.\" ====================================================================
.
The table format specification is mandatory:
it determines the number of columns in the table and directs how the
entries within it are to be typeset.
.
The format specification is a series of column
.I descriptors.
.
Each descriptor encodes a
.I classifier
followed by zero or more
.I modifiers.
.
Classifiers are letters
(recognized case-insensitively)
or punctuation symbols;
modifiers consist of or begin with letters or numerals.
.
Spaces,
tabs,
newlines,
and commas separate descriptors.
.
Newlines and commas are special;
they apply the descriptors following them to a subsequent row of the
table.
.
(This enables column headings to be centered or emboldened while the
table entries for the data are not,
for instance.)
.
We term the resulting group of column descriptors a
.I row definition.
.
Within a row definition,
separation between column descriptors
(by spaces or tabs)
is often optional;
only some modifiers,
described below,
make separation necessary.
.
.
.P
Each column descriptor begins with a mandatory
.I classifier,
a character that selects from one of several arrangements.
.
Some determine the positioning of table entries within a rectangular
cell:
centered,
left-aligned,
numeric
(aligned to a configurable decimal separator),
and so on.
.
Others perform special operations like drawing lines or spanning entries
from adjacent cells in the table.
.
Except for
.RB \[lq] | \[rq],
any classifier can be followed by one or more
.I modifiers;
some of these accept an argument,
which in GNU
.I tbl \" GNU
can be parenthesized.
.\" AT&T tbl allowed parentheses only after 'w'.
.\" TODO: Accept parentheses after 'p' and 'v'.
.
Modifiers select fonts,
set the type size,
.\"define the column width,
.\"adjust inter-column spacing, \" slack text for window/orphan control
and perform other tasks described below.
.
.
.P
The format specification can occupy multiple input lines,
but must conclude with a dot
.RB \[lq] .\& \[rq]
followed by a newline.
.
Each row definition is applied in turn to one row of the table.
.
The last row definition is applied to rows of table data in excess of
the row definitions.
.
.
.P
For clarity in this document's examples,
we shall write classifiers in uppercase and modifiers in lowercase.
.
Thus,
.RB \[lq] CbCb,LR.\& \[rq]
defines two rows of two columns.
.
The first row's entries are centered and boldfaced;
the second and any further rows' first and second columns are left- and
right-aligned,
respectively.
.
.\" slack text for window/orphan control
.\"If more rows of entries are added to the table data,
.\"they reuse the row definition
.\".RB \[lq] LR \[rq].
.
.
.P
The row definition with the most column descriptors determines the
number of columns in the table;
any row definition with fewer is implicitly extended on the right-hand
side with
.B L
classifiers as many times as necessary to make the table rectangular.
.
.
.\" ====================================================================
.SS "Column classifiers"
.\" ====================================================================
.
The
.BR L ,
.BR R ,
and
.B C
classifiers are the easiest to understand and use.
.
.
.TP
.BR A ,\~ a
Center longest entry in this column,
left-align remaining entries in the column with respect to the centered
entry,
then indent all entries by one en.
.
Such \[lq]alphabetic\[rq] entries
(hence the name of the classifier)
can be used in the same column as
.BR L -classified
entries,
as in
.RB \[lq] LL,AR.\& \[rq].
.
The
.B A
entries are often termed \[lq]sub-columns\[rq] due to their indentation.
.
.
.TP
.BR C ,\~ c
Center entry within the column.
.
.
.TP
.BR L ,\~ l
Left-align entry within the column.
.
.
.TP
.BR N ,\~ n
Numerically align entry in the column.
.
.I @g@tbl
aligns columns of numbers vertically at the units place.
.
If multiple decimal separators are adjacent to a digit,
it uses the rightmost one for vertical alignment.
.
If there is no decimal separator,
the rightmost digit is used for vertical alignment;
otherwise,
.I @g@tbl
centers the entry within the column.
.
The
.I roff
dummy character
.B \[rs]&
in an entry marks the glyph preceding it
(if any)
as the units place;
if multiple instances occur in the data,
the leftmost is used for alignment.
.
.
.IP
If
.BR N -classified
entries share a column with
.B L
or
.BR R \~entries,
.I @g@tbl
centers the widest
.BR N \~entry
with respect to the widest
.B L
or
.BR R \~entry,
preserving the alignment of
.BR N \~entries
with respect to each other.
.
.
.IP
The appearance of
.I @g@eqn
equations
within
.BR N -classified
columns
can be troublesome due to the foregoing textual scan for a decimal
separator.
.
Use the
.B \%delim
region option to make
.I @g@tbl
ignore the data within
.I eqn
delimiters for that purpose.
.
.
.TP
.BR R ,\~ r
Right-align entry within the column.
.
.
.TP
.BR S ,\~ s
Span previous entry on the left into this column.
.
.
.TP
.B \[ha]
Span entry in the same column from the previous row into this row.
.
.
.TP
.BR _ ,\~ \-
Replace table entry with a horizontal rule.
.
An empty table entry is expected to correspond to this classifier;
if data are found there,
.I @g@tbl
issues a diagnostic message.
.
.
.TP
.B =
Replace table entry with a double horizontal rule.
.
An empty table entry is expected to correspond to this classifier;
if data are found there,
.I @g@tbl
issues a diagnostic message.
.
.
.TP
.B |
Place a vertical rule (line) on the corresponding row of the table
(if two of these are adjacent,
a double vertical rule).
.
This classifier does not contribute to the column count and no table
entries correspond to it.
.
A
.B |
to the left of the first column descriptor or to the right of the last
one produces a vertical rule at the edge of the table;
these are redundant
(and ignored)
in boxed tables.
.
.
.P
To change the table format within a
.I @g@tbl
region,
use the
.B .T&
token at the start of a line.
.
It is followed by a format specification and table data,
but
.I not
region options.
.
The quantity of columns in a new table format thus introduced cannot
increase relative to the previous table format;
in that case,
you must end the table region and start another.
.
If that will not serve because the region uses box options or the
columns align in an undesirable manner,
you must design the initial table format specification to include the
maximum quantity of columns required,
and use the
.B S
horizontal spanning classifier where necessary to achieve the desired
columnar alignment.
.
.
.P
Attempting to horizontally span in the first column or vertically span
on the first row is an error.
.
Non-rectangular span areas are also not supported.
.
.
.\" ====================================================================
.SS "Column modifiers"
.\" ====================================================================
.
Any number of modifiers can follow a column classifier.
.
Arguments to modifiers,
where accepted,
are case-sensitive.
.
If the same modifier is applied to a column specifier more than once,
or if conflicting modifiers are applied,
only the last occurrence has effect.
.
The
.RB modifier\~ x
is mutually exclusive with
.B e
.RB and\~ w ,
but
.B e
is not mutually exclusive
.RB with\~ w ;
if these are used in combination,
.BR x \~unsets
both
.B e
.RB and\~ w ,
while either
.B e
or
.B w
.RB overrides\~ x .
.
.
.br
.ne 4v \" Keep next two tagged paragraphs together.
.TP
.BR b ,\~ B
Typeset entry in boldface,
abbreviating
.BR f(B) .
.
.
.TP
.BR d ,\~ D
Align a vertically spanned table entry to the bottom
(\[lq]down\[rq]),
instead of the center,
of its range.
.
This is a GNU extension.
.
.
.TP
.BR e ,\~ E
Equalize the widths of columns with this modifier.
.
The column with the largest width controls.
.
This modifier sets the default line length used in a text block.
.
.
.TP
.BR f ,\~ F
Select the typeface for the table entry.
.
This modifier must be followed by a font or style name
(one or two characters not starting with a digit),
font mounting position
(a single digit),
or a name or mounting position of any length in parentheses.
.
The last form is a GNU extension.
.
(The parameter corresponds to that accepted by the
.I troff \" generic
.B ft
request.)
.
A one-character argument not in parentheses must be separated by one or
more spaces or tabs from what follows.
.
.
.TP
.BR i ,\~ I
Typeset entry in an oblique or italic face,
abbreviating
.BR f(I) .
.
.
.TP
.BR m ,\~ M
Call a
.I groff
macro before typesetting a text block
(see subsection \[lq]Text blocks\[rq] below).
.
This is a GNU extension.
.
This modifier must be followed by a macro name of one or two characters
or a name of any length in parentheses.
.
A one-character macro name not in parentheses must be separated by one
or more spaces or tabs from what follows.
.
The named macro must be defined before the table region containing this
column modifier is encountered.
.
The macro should contain only simple
.I groff
requests to change text formatting,
like adjustment or hyphenation.
.
The macro is called
.I after
the column modifiers
.BR b ,
.BR f ,
.BR i ,
.BR p ,
and
.B v
take effect;
it can thus override other column modifiers.
.
.
.TP
.BR p ,\~ P
Set the type size for the table entry.
.
This modifier must be followed by an
.RI integer\~ n
with an optional leading sign.
.
If unsigned,
the type size is set to
.IR n \~scaled
points.
.
Otherwise,
the type size is incremented or decremented per the sign by
.IR n \~scaled
points.
.
The use of a signed multi-digit number is a GNU extension.
.
(The parameter corresponds to that accepted by the
.I troff \" generic
.B ps
request.)
.
If a type size modifier is followed by a column separation modifier
(see below),
they must be separated by at least one space or tab.
.\" TODO: Allow parentheses so scaling units and fractional values can
.\" be used?
.
.
.TP
.BR t ,\~ T
Align a vertically spanned table entry to the top,
instead of the center,
of its range.
.
.
.TP
.BR u ,\~ U
Move the column up one half-line,
\[lq]staggering\[rq] the rows.
.
This is a GNU extension.
.
.
.TP
.BR v ,\~ V
Set the vertical spacing to be used in a text block.
.
This modifier must be followed by an
.RI integer\~ n
with an optional leading sign.
.
If unsigned,
the vertical spacing is set to
.IR n\~ points.
.
Otherwise,
the vertical spacing is incremented or decremented per the sign by
.IR n\~ points.
.
The use of a signed multi-digit number is a GNU extension.
.
(This parameter corresponds to that accepted by the
.I troff \" generic
.B vs
request.)
.
If a vertical spacing modifier is followed by a column separation
modifier
(see below),
they must be separated by at least one space or tab.
.\" TODO: Allow parentheses so scaling units and fractional values can
.\" be used?
.
.
.TP
.BR w ,\~ W
Set the column's minimum width.
.
This modifier must be followed by a number,
which is either a unitless integer,
or a
.I roff
horizontal measurement in parentheses.
.
Parentheses are required if the width is to be followed immediately by
an explicit column separation
(alternatively,
follow the width with one or more spaces or tabs).
.
If no unit is specified,
ens are assumed.
.
This modifier sets the default line length used in a text block.
.
.
.TP
.BR x ,\~ X
Expand the column.
.
After computing the column widths,
distribute any remaining line length evenly over all columns bearing
this modifier.
.
Applying the
.BR x \~modifier
to more than one column is a GNU extension.
.\" 'x' wasn't documented at all in Lesk 1979.
.
This modifier sets the default line length used in a text block.
.
.
.TP
.BR z ,\~ Z
Ignore the table entries corresponding to this column for width
calculation purposes;
that is,
compute the column's width using only the information in its descriptor.
.
.
.TP
.I n
A numeric suffix on a column descriptor sets the separation distance
(in ens)
from the succeeding column;
the default separation is
.BR 3n .
.
This separation is
proportionally multiplied if the
.B expand
region option is in effect;
in the case of tables wider than the output line length,
this separation might be zero.
.
A negative separation cannot be specified.
.
A separation amount after the last column in a row is nonsensical and
provokes a diagnostic from
.IR @g@tbl .
.
.
.\" ====================================================================
.SS "Table data"
.\" ====================================================================
.
The table data come after the format specification.
.
Each input line corresponds to a table row,
except that a backslash at the end of a line of table data continues an
entry on the next input line.
.
(Text blocks,
discussed below,
also spread table entries across multiple input lines.)
.
Table entries within a row are separated in the input by a tab character
by default;
see the
.B tab
region option above.
.
Excess entries in a row of table data
(those that have no corresponding column descriptor,
not even an implicit one arising from rectangularization of the table)
are discarded with a diagnostic message.
.
.I roff
control lines are accepted between rows of table data and within text
blocks.
.
If you wish to visibly mark an empty table entry in the document source,
populate it with the
.B \[rs]&
.I roff
dummy character.
.
The table data are interrupted by a line consisting of the
.B .T&
input token,
and conclude with the line
.BR .TE .
.
.
.P
Ordinarily,
a table entry is typeset rigidly.
.
It is not filled,
broken,
hyphenated,
adjusted,
or populated with additional inter-sentence space.
.
.I @g@tbl
instructs the formatter to measure each table entry as it occurs in the
input,
updating the width required by its corresponding column.
.
If the
.B z
modifier applies to the column,
this measurement is ignored;
if
.B w
applies and its argument is larger than this width,
that argument is used instead.
.
In contrast to conventional
.I roff
input
(within a paragraph,
say),
changes to text formatting,
such as font selection or vertical spacing,
do not persist between entries.
.
.
.P
Several forms of table entry are interpreted specially.
.
.
.IP \[bu] 2n
If a table row contains only an underscore or equals sign
.RB ( _
or
.BR = ),
a single or double horizontal rule (line),
respectively,
is drawn across the table at that point.
.
.
.IP \[bu] 2n
A table entry containing only
.B _
or
.B =
on an otherwise populated row is replaced by a single or double
horizontal rule,
respectively,
joining its
neighbors.
.
.
.IP \[bu] 2n
Prefixing a lone underscore or equals sign with a backslash also has
meaning.
.
If a table entry consists only of
.B \[rs]_
or
.B \[rs]=
on an otherwise populated row,
it is replaced by a single or double horizontal rule,
respectively,
that does
.I not
(quite) join its neighbors.
.
.
.IP \[bu]
A table entry consisting of
.BI \[rs]R x\c
,
where
.IR x \~is
any
.I roff
ordinary or special character,
is replaced by enough repetitions of the glyph corresponding
.RI to\~ x
to fill the column,
albeit without joining its neighbors.
.\" TODO: Bad things happen if there's garbage in the entry after 'x',
.\" which can be a *roff special character escape sequence, so
.\" validation is not trivial.
.
.
.IP \[bu]
On any row but the first,
a table entry of
.B \[rs]\[ha]
causes the entry above it to span down into the current one.
.
.
.P
On occasion,
these special tokens may be required as literal table data.
.
To use either
.B _
or
.B =
literally and alone in an entry,
prefix or suffix it with the
.I roff
dummy character
.BR \[rs]& .
.
To express
.BR \[rs]_ ,
.BR \[rs]= ,
or
.BR \[rs]R ,
use a
.I roff
escape sequence to interpolate the backslash
.RB ( \[rs]e
or
.BR \[rs][rs] ).
.
A reliable way to emplace the
.B \[rs]\[ha]
glyph sequence within a table entry is to use a pair of
.I groff
special character escape sequences
.RB ( \[rs][rs]\[rs][ha] ).
.
.
.P
Rows of table entries can be interleaved with
.I groff
control lines;
these do not count as table data.
.
On such lines the default control character
.RB ( .\& )
must be used
(and not changed);
the no-break control character is not recognized.
.
To start the first table entry in a row with a dot,
precede it with the
.I roff
dummy character
.BR \[rs]& .
.
.
.\" ====================================================================
.SS "Text blocks"
.\" ====================================================================
.
An ordinary table entry's contents can make a column,
and therefore the table,
excessively wide;
the table then exceeds the line length of the page,
and becomes ugly or is exposed to truncation by the output device.
.
When a table entry requires more conventional typesetting,
breaking across more than one output line
(and thereby increasing the height of its row),
it can be placed within a
.I text block.
.
.
.P
.I @g@tbl
interprets a table entry beginning with
.RB \[lq] T{ \[rq]
at the end of an input line not as table data,
but as a token starting a text block.
.
Similarly,
.RB \[lq] T} \[rq]
at the start of an input line ends a text block;
it must also end the table entry.
.
Text block tokens can share an input line with other table data
(preceding
.B T{
and following
.BR T} ).
.
Input lines between these tokens are formatted in a diversion by
.IR troff . \" generic
.
Text blocks cannot be nested.
.
Multiple text blocks can occur in a table row.
.
.
.P
Text blocks are formatted as was the text prior to the table,
modified by applicable column descriptors.
.
Specifically,
the classifiers
.BR A ,
.BR C ,
.BR L ,
.BR N ,
.BR R ,
and
.B S
determine a text block's
.I alignment
within its cell,
but not its
.I adjustment.
.
Add
.B na
or
.B ad
requests to the beginning of a text block to alter its adjustment
distinctly from other text in the document.
.
As with other table entries,
when a text block ends,
any alterations to formatting parameters are discarded.
.
They do not affect subsequent table entries,
not even other text blocks.
.
.
.P
.ne 2v
If
.B w
or
.B x
modifiers are not specified for
.I all
columns of a text block's span,
the default length of the text block
(more precisely,
the line length used to process the text block diversion)
is computed as
.IR L \[tmu] C /( N +1),
.\" ...and rounded to the horizontal motion quantum of the output device
where
.I L
is the current line length,
.I C
the number of columns spanned by the text block,
and
.I N
the number of columns in the table.
.
If necessary,
you can also control a text block's width by including an
.B ll
(line length)
request in it prior to any text to be formatted.
.
Because a diversion is used to format the text block,
its height and width are subsequently available in the registers
.B dn
and
.BR dl ,
respectively.
.
.
.\" ====================================================================
.SS \f[I]roff\f[] interface
.\" ====================================================================
.
The register
.B TW
stores the width of the table region in basic units;
it can't be used within the region itself,
but is defined before the
.B .TE
token is output so that a
.I groff
macro named
.B TE
can make use of it.
.
.B T.\&
is a Boolean-valued register indicating whether the bottom of the table
is being processed.
.
The
.B #T
register marks the top of the table.
.
Avoid using these names for any other purpose.
.
.
.P
.I @g@tbl
also defines a macro
.B T#
to produce the bottom and side lines of a boxed table.
.
While
.I @g@tbl
itself arranges for the output to include a call of this macro at the
end of such a table,
it can also be used by macro packages to create boxes for multi-page
tables by calling it from a page footer macro that is itself called by
a trap planted near the bottom of the page.
.
See section \[lq]Limitations\[rq] below for more on multi-page tables.
.
.
.P
GNU
.I tbl \" GNU
.\" AT&T tbl used all kinds of registers; many began with "3".
internally employs register,
string,
macro,
and diversion names beginning with the
.RB numeral\~ 3 .
.
A document to be preprocessed with GNU
.I tbl \" GNU
should not use any such identifiers.
.\" XXX: Why are they not named starting with "gtbl*" or something?  GNU
.\" tbl turns AT&T troff compatibility mode off anyway.
.
.
.\" ====================================================================
.SS "Interaction with \f[I]@g@eqn\f[]"
.\" ====================================================================
.
.I @g@tbl
should always be called before
.MR @g@eqn @MAN1EXT@ .
.
(\c
.MR groff @MAN1EXT@
automatically arranges preprocessors in the correct order.)
.
Don't call the
.B EQ
and
.B EN
macros within tables;
instead,
set up delimiters in your
.I eqn \" generic
input and use the
.B \%delim
region option so that
.I @g@tbl
will recognize them.
.
.
.br
.ne 5v \" Keep enough space for heading, intro sentence, and first item.
.\" ====================================================================
.SS "GNU \f[I]tbl\f[] enhancements"
.\" ====================================================================
.
In addition to extensions noted above,
GNU
.I tbl \" GNU
removes constraints endured by users of AT&T
.IR tbl .\" AT&T
.
.
.IP \[bu] 2n
Region options can be specified in any lettercase.
.
.
.IP \[bu]
There is no limit on the number of columns in a table,
regardless of their classification,
nor any limit on the number of text blocks.
.
.
.IP \[bu]
All table rows are considered when deciding column widths,
not just those occurring in the first 200 input lines of a region.
.
Similarly,
table continuation
.RB ( .T& )
tokens are recognized outside a region's first 200 input lines.
.
.
.IP \[bu]
Numeric and alphabetic entries may appear in the same column.
.
.
.IP \[bu]
Numeric and alphabetic entries may span horizontally.
.
.
.\" ====================================================================
.SS "Using GNU \f[I]tbl\f[] within macros"
.\" ====================================================================
.
You can embed a table region inside a macro definition.
.
However,
since
.I @g@tbl
writes its own macro definitions at the beginning of each table region,
it is necessary to call end macros instead of ending macro definitions
with
.RB \[lq] ..\& \[rq].
.\" XXX: Why don't we fix that by ending all of tbl's own macro
.\" definitions with a call to a macro in its own reserved name space?
.
Additionally,
the escape character must be disabled. \" XXX: Why?
.
.
.P
Not all
.I @g@tbl
features can be exercised from such macros because
.I @g@tbl
is a
.I roff
preprocessor:
it sees the input earlier than
.I @g@troff
does.
.
For example,
vertically aligning decimal separators fails if the numbers containing
them occur as macro or string parameters;
the alignment is performed by
.I @g@tbl
itself,
which sees only
.BR \[rs]$1 ,
.BR \[rs]$2 ,
and so on,
and therefore can't recognize a decimal separator that only appears
later when
.I @g@troff
interpolates a macro or string definition.
.
.
.\" XXX: The following is a general caveat about preprocessors; move it.
.P
Using
.I @g@tbl
macros within conditional input
(that is,
contingent upon an
.BR if ,
.BR ie ,
.BR el ,
or
.B while
request)
can result in misleading line numbers in subsequent diagnostics.
.
.I @g@tbl
unconditionally injects its output into the source document,
but the conditional branch containing it may not be taken,
and if it is not,
the
.B lf
requests that
.I @g@tbl
injects to restore the source line number cannot take effect.
.
Consider copying the input line counter register
.B c.\&
and restoring its value at a convenient location after applicable
arithmetic.
.
.
.br
.ne 5v
.\" ====================================================================
.SH Options
.\" ====================================================================
.
.B \-\-help
displays a usage message,
while
.B \-v
and
.B \-\-version
show version information;
all exit afterward.
.
.
.TP
.B \-C
Enable AT&T compatibility mode:
recognize
.B .TS
and
.B .TE
even when followed by a character other than space or newline.
.
Furthermore,
interpret the uninterpreted leader escape sequence
.BR \[rs]a .
.
.
.\" ====================================================================
.SH Limitations
.\" ====================================================================
.
Multi-page tables,
if boxed and/or if you want their column headings repeated after page
breaks,
require support at the time the document is formatted.
.
A convention for such support has arisen in macro packages such as
.IR ms ,
.IR mm ,
and
.IR me .
.
To use it,
follow the
.B .TS
token with a space and then
.RB \[lq] H \[rq];
this will be interpreted by the formatter
as a
.B TS
macro call with an
.B H
argument.
.
Then,
within the table data,
call the
.B TH
macro;
this informs the macro package where the headings end.
.
If your table has no such heading rows,
or you do not desire their repetition,
call
.B TH
immediately after the table format specification.
.
If a multi-page table is boxed or has repeating column headings,
do not enclose it with keep/release macros,
or divert it in any other way.
.
Further,
the
.B bp
request will not cause a page break in a
.RB \[lq] "TS H" \[rq]
table.
.
Define a macro to wrap
.BR bp :
invoke it normally if there is no current diversion.
.
Otherwise,
pass the macro call to the enclosing diversion using the transparent
line escape sequence
.BR \[rs]!\& ;
this will \[lq]bubble up\[rq] the page break to the output device.
.
See section \[lq]Examples\[rq] below for a demonstration.
.
.
.P
Double horizontal rules are not supported by
.MR grotty @MAN1EXT@ ;
single rules are used instead.
.
.I \%grotty
also ignores half-line motions,
so the
.B u
column modifier has no effect.
.
On terminal devices
.RI (\[lq] nroff\~ mode\[rq]),
horizontal rules and box borders occupy a full vee of space;
this amount is doubled for
.B doublebox
tables.
.
Tables using these features thus require more vertical space in
.I nroff
mode than in
.I troff
mode:
write
.B ne
requests accordingly.
.
Vertical rules between columns are drawn in the space between columns in
.I nroff
mode;
using double vertical rules and/or reducing the column separation below
the default can make them ugly or overstrike them with table data.
.
.
.P
A text block within a table must be able to fit on one page.
.
.
.P
Using
.B \[rs]a
to put leaders in table entries does not work
in GNU
.IR tbl , \" GNU
except in compatibility mode.
.
This is correct behavior:
.B \[rs]a
is an
.I uninterpreted
leader.
.
You can still use the
.I roff
leader character (Control+A) or define a string to use
.B \[rs]a
as it was designed:
to be interpreted only in copy mode.
.
.
.RS
.P
.EX
\&.ds a \[rs]a
\&.TS
\&box center tab(;);
\&Lw(2i)0 L.
\&Population\[rs]*a;6,327,119
\&.TE
.EE
.RE
.
.
.\" We use a real leader to avoid defining a string in a man page.
.P
.TS
box center tab(;);
Lw(2i)0 L.
Population
;6,327,119
.TE
.
.
.P
A leading and/or trailing
.B |
in a format specification,
such as
.RB \[lq] |LCR|.\& \[rq],
produces an en space between the vertical rules and the content of the
adjacent columns.
.
If no such space is desired
(so that the rule abuts the content),
you can introduce \[lq]dummy\[rq] columns with zero separation and empty
corresponding table entries before and/or after.
.
.
.RS
.P
.EX
\&.TS
\&center tab(#);
\&R0|L C R0|L.
_
\&#levulose#glucose#dextrose#
_
\&.TE
.EE
.RE
.
.
.P
These dummy columns have zero width and are therefore invisible;
unfortunately they usually don't work as intended on terminal devices.
.
.
.if t \{\
.TS
center tab(#);
R0|L C R0|L.
_
#levulose#glucose#dextrose#
_
.TE
.\}
.
.
.\" ====================================================================
.SH Examples
.\" ====================================================================
.
It can be easier to acquire the language of
.I tbl \" generic
through examples than formal description,
especially at first.
.
.
.\" Note: This example is nearly at the column limit (78n) for nroff
.\" output.  Recast with care.
.RS
.P
.EX
\&.TS
box center tab(#);
Cb Cb
L L.
Ability#Application
Strength#crushes a tomato
Dexterity#dodges a thrown tomato
Constitution#eats a month-old tomato without becoming ill
Intelligence#knows that a tomato is a fruit
Wisdom#chooses \[rs]f[I]not\[rs]f[] to put tomato in a fruit salad
Charisma#sells obligate carnivores tomato-based fruit salads
\&.TE
.EE
.RE
.
.
.P
.TS
box center tab(#);
Cb Cb
L L.
Ability#Application
Strength#crushes a tomato
Dexterity#dodges a thrown tomato
Constitution#eats a month-old tomato without becoming ill
Intelligence#knows that a tomato is a fruit
Wisdom#chooses \f[I]not\f[] to put tomato in a fruit salad
Charisma#sells obligate carnivores tomato-based fruit salads
.TE
.
.
.P
The
.B A
and
.B N
column classifiers can be easier to grasp in visual rendering than in
description.
.
.
.RS
.P
.EX
\&.TS
center tab(;);
CbS,LN,AN.
Daily energy intake (in MJ)
Macronutrients
\&.\[rs]" assume 3 significant figures of precision
Carbohydrates;4.5
Fats;2.25
Protein;3
\&.T&
LN,AN.
Mineral
Pu\-239;14.6
_
\&.T&
LN.
Total;\[rs][ti]24.4
\&.TE
.EE
.RE
.
.
.RS
.P
.TS
center tab(;);
CbS,LN,AN.
Daily energy intake (in MJ)
.\" assume 3 significant figures of precision
Macronutrients
Carbohydrates;4.5
Fats;2.25
Protein;3
.T&
LN,AN.
Mineral
Pu-239;14.6
_
.T&
LN.
Total;\[ti]24.4
.TE
.RE
.
.
.br
.ne 12v
.P
Next,
we'll lightly adapt a compact presentation of spanning,
vertical alignment,
and zero-width column modifiers from the
.I mandoc
reference for its
.I tbl \" generic
interpreter.
.
It rewards close study.
.
.
.RS
.P
.EX
\&.TS
box center tab(:);
Lz  S | Rt
Ld| Cb| \[ha]
\[ha] | Rz  S.
left:r
l:center:
:right
\&.TE
.EE
.RE
.
.
.RS
.P
.TS
box center tab(:);
Lz  S | Rt
Ld| Cb| ^
^ | Rz  S.
left:r
l:center:
:right
.TE
.RE
.
.
.P
.ne 2v
Row staggering is not visually achievable on terminal devices,
but a table using it can remain comprehensible nonetheless.
.
.
.RS
.P
.EX
\&.TS
center tab(|);
Cf(BI) Cf(BI) Cf(B), C C Cu.
n|n\[rs]f[B]\[rs][tmu]\[rs]f[]n|difference
1|1
2|4|3
3|9|5
4|16|7
5|25|9
6|36|11
\&.TE
.EE
.RE
.
.
.RS
.P
.TS
center tab(|);
Cf(BI) Cf(BI) Cf(B), C C Cu.
n|n\f[B]\[tmu]\f[]n|difference
1|1
2|4|3
3|9|5
4|16|7
5|25|9
6|36|11
.TE
.RE
.
.
.P
Some
.I @g@tbl
features cannot be illustrated in the limited environment of a portable
man page.
.
.
.\" TODO: Find a better example than this.
.\".P
.\"As noted above,
.\"we can embed a table region in a
.\".I groff
.\"macro definition.
.\".
.\".IR @g@tbl ,
.\"however,
.\"cannot know what will result from any macro argument interpolations,
.\"so we might confine such interpolations to one column of the table and
.\"apply the
.\".B x
.\"modifier to it.
.\".
.\".
.\".RS
.\".P
.\".EX
.\"\&.de END
.\"\&..
.\"\&.eo
.\"\&.de MYTABLE END
.\"\&.TS
.\"\&allbox tab(;);
.\"\&C Lx.
.\"\&This is table \[rs]$1.;\[rs]$2
.\"\&.TE
.\"\&.END
.\"\&.ec
.\"\&.MYTABLE 1 alpha
.\"\&.MYTABLE 2 beta
.\"\&.MYTABLE 3 "gamma delta"
.\".EE
.\".RE
.\"
.\"
.P
We can define a macro outside of a
.I tbl \" generic
region that we can call from within it to cause a page break inside a
multi-page boxed table.
.
You can choose a different name;
be sure to change both occurrences of \[lq]BP\[rq].
.
.
.RS
.P
.ne 4v
.EX
\&.de BP
\&.\&  ie \[aq]\[rs]\[rs]n(.z\[aq]\[aq] \&.bp \[rs]\[rs]$1
\&.\&  el \[rs]!.BP \[rs]\[rs]$1
\&..
.EE
.RE
.
.
.\" ====================================================================
.SH "See also"
.\" ====================================================================
.
\[lq]Tbl\[em]A Program to Format Tables\[rq],
by M.\& E.\& Lesk,
1976
(revised 16 January 1979),
AT&T Bell Laboratories Computing Science Technical Report No.\& 49.
.
.
.P
The spanning example above was taken from
.UR https://man.openbsd.org/tbl.7
.IR mandoc 's
man page for its
.I tbl \" mandoc
implementation
.UE .
.
.
.P
.MR groff @MAN1EXT@ ,
.MR @g@troff @MAN1EXT@
.
.
.\" Restore compatibility mode (for, e.g., Solaris 10/11).
.cp \n[*groff_tbl_1_man_C]
.do rr *groff_tbl_1_man_C
.
.
.\" Local Variables:
.\" fill-column: 72
.\" mode: nroff
.\" End:
.\" vim: set filetype=groff textwidth=72: