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DEFINITIONS OF TERMS USED IN THIS MANUAL
Mom Document Processing Terms
I use a number of typesetting-specific and groff-specific terms
throughout this documentation, as well as a few terms that apply
to mom herself. To make life easier, I'll explain
them here. Refer back to this section should you encounter a word
or concept you're not familiar with.
- The portion of a letter that extends above the bowl. For example,
the letters a, c, and e have no ascenders. The letters b, d, and h
- The imaginary line on which the bottoms of capital letters and the
bowls of lower case letters rest.
- Ballot box
- An unfilled square, usually
in size, typically placed beside items in a checklist.
- A small, filled circle typically found beside items or points in
- The height of the tallest capital letter in a given
at the current
- The portion of a letter that extends beneath the
(j, q, y are letters with descenders).
- Discretionary hyphen
- A symbol inserted between two syllables of a word that indicates to a
typesetting program the legal hyphenation points in the word. Normally,
if hyphenation is turned on, groff knows where to hyphenate words.
However, hyphenation being what it is (in English, at any rate),
groff doesn't always get it right. Discretionary hyphens make sure
it does. In the event that the word doesn't need to be hyphenated
at all, groff leaves them alone. In groff, the discretionary hyphen is
(backslash followed by a percent).
- Drop cap
- A large, usually upper-case letter that introduces the first
paragraph of a document or section thereof. The top of the drop
cap usually lines up with the top of the first line of the
paragraph, and typically "drops" several lines lower.
Text adjacent to the drop cap is indented to the right of the
letter until the bottom of the drop cap is reached, at which
point text reverts to the left margin.
- An em is a relative measurement equal to the width of the
letter M at a given
in a given
Since most Ms are designed square, an em is usually (but sometimes
erroneously) considered to be the same size as the current point
size (i.e. if the point size of the type is 12, one em equals 12
points). An en is equal to the width of a letter N (historically
2/3 of an em, although groff treats an en as 1/2 of an em).
Typically, ems and ens are used to measure indents, or to define the
length of dashes (long hyphens).
- The collective name by which a collection of
are known, e.g. Helvetica, Times Roman, Garamond.
- Figure space/Digit space
fixed width space
that has the width of one digit. Used for aligning numerals in,
say, columns or numbered lists. In groff, the figure space is
(backslash followed by a zero).
- Fixed width space
- Equal to
but does not expand or contract when text is
In groff, fixed width space is entered with
where <space> means "hit the spacebar on your keyboard."
- The specific
of type within a
e.g. light, medium, bold (which are weights), and roman, italic,
condensed (which are shapes). By default, groff knows of four fonts
within its default set of families: R (medium roman), I (medium
italic), B (bold roman) and BI (bold italic).
- Force justify
- Sometimes, in
text, a line needs to be broken short of the right margin. Force
justifying means telling a typesetting program (like groff) that you
want the line broken early AND that you want the line's word spacing
stretched to force the line flush with the right margin.
- The vertical whitespace separating columns of type.
- Lines of type are justified when they're flush at both the left and
right margins. Justification is the act of making both margins flush.
Some people use the terms "left justified" and "right justified"
to mean type where only the left (or right) margins align. I don't.
- Moving pairs of letters closer together to remove excess
whitespace between them. In the days before phototypesetting,
type was set from small, rectangular blocks of wood or metal, each
block having exactly one letter. Because the edge of each block
determined the edge of each letter, certain letter combinations (TA,
for example) didn't fit together well and had to be mortised by hand
to bring them visually closer. Modern typesetting systems usually
take care of kerning automatically, but they're far from perfect.
Professional typesetters still devote a lot of time to fitting letters
and punctuation together properly.
- Kern Units
- A relative distance equal to 1/36 of the current
Used between individual letters
Different typesetting systems use different values (1/54 is
popular), and sometimes call kern units by a different name.
A kern unit has nothing to do with groff
- The distance from the
of one line of type to the line of type immediately beneath it.
Pronounced "ledding." Also called line spacing. Usually measured
In case you're interested... In previous centuries,
lines of type were separated by thin strips of--you guessed
it--lead. Lines of type that had no lead between them were said to
be "set solid." Once you began separating them with strips
of lead, they were said to be "leaded", and the spacing was
expressed in terms of the number of
of lead. For this reason, "leading" and "line
spacing" aren't, historically speaking, synonymous. If type
was set 10 on 12, for example, the leading was 2 points, not 12.
Nowadays, however, the two terms are used interchangeably to mean
the distance from baseline to baseline.
- Single characters used to fill lines, usually to their end.
So called because they "lead" the eye from one element
of the page to another. For example, in the following (brief)
Table of Contents, the periods (dots) are leaders.
Chapter 1.............. 5
Chapter 2.............. 38
Chapter 3.............. 60
- Ligatures are letters joined together to form a single character.
The commonest are fi, fl, ff, ffi and ffl. Others are ae and oe.
Occasionally, one sees an st ligature, but this is archaic and
- There are twelve points in a pica, and six picas in an inch
(hence 72 points to the inch). In the same way that gem-dealers
have always used their own system of measurement for weight (carats),
typographers have always used their own system of measurement for type.
- Point Size
- The nominal size of type, measured in
from the bottom of the longest
to the top of the highest
In reality, type is always fractionally smaller than its point size.
- When only one margin of type is flush, lines of type are quadded in
the direction of the flush margin. Therefore, quad left means the
left margin is flush, the right isn't. Quad right means the right
margin is flush, the left isn't. Quad centre means neither the left
nor the right margin is flush; rather, lines of type are quadded on
both sides so that type appears centred on the page.
- Describes a margin that isn't flush. Rag right means the right
margin isn't flush. Rag left means the left margin isn't flush.
The expression "flush left/rag right" is sometimes used to describe
type that is
- The degree of slant and/or the width of characters.
(Technically speaking, this is not a proper typesetting term;
however, it may help clarify some concepts presented in these
Some typical shapes are:
as it is used in these documents, refers to a combination of
- "Roman", which has no slant, and has letterforms of
- "Italic", which is slanted, and has letterforms
of average width
- "Condensed", which has no slant, but has
letterforms narrower than the average represented by Roman
- "Condensed Italic", which is slanted, with letterforms narrower
- Solid/set solid
- When no
is added between lines of type (i.e. the
and linespacing are the same), the lines are said to be "set
- Track kerning/Line kerning
- Sometimes, it's advantageous to increase or decrease the amount of
space between every letter in a line by an equal (usually small)
amount, in order to fit more (or fewer) characters on the line.
The correct term is letter spacing, but track kerning and line kerning
(and sometimes, just "kerning") have come to mean the same thing.
- Unbreakable space
- Equal to
however words separated by an unbreakable space will always be kept
together on the same line. Expands and contracts like word space.
Useful for proper names, which one should, whenever possible, avoid
splitting onto two lines. In groff, unbreakable space is entered
(backslash followed by a tilde).
- The thickness of the strokes of letterforms. Medium and Book
have average thicknesses and are the weights used for most of the
text in books, magazines, newspapers, etc. Light has strokes
slightly thinner than Medium or Book, but is still acceptable for
most text. Semibold, Bold, Heavy and Black all have strokes of
increasing thickness, making them suitable for heads, subheads,
headlines and the like.
- Word space
- The amount of whitespace between words. When text is
word space expands or contracts to make the margins flush.
- The height of a lower case letter x in a given font at a given
point size. Generally used to mean the average height of the bowl
of lower case letters.
invoked by a name different from its "official"
name. For example, the official name of the macro to change
is FAMILY. Its alias is
FAM. Aliases may be created for any macro (via the
macro) provided the alias uses a name not already taken
by the mom macros or one of the groff
For a complete list of words or names you must not use, see the
list of reserved words.
- Parameters or information needed by a
to do its job. For example, in the macro
"12" is the argument. In the macro
LEFT is the argument. Arguments are separated from macros by spaces.
Some macros require several arguments; each is separated by a space.
- Comment Lines
- Input lines
introduced with the comment character
When processing output, groff silently ignores everything on a
line that begins with the comment character.
- Control Lines
- Instructions to groff that appear on a line by themselves,
which means that "control lines" are either
Control lines begin with a period or, occasionally, an apostrophe.
- Filled lines/fill mode
In fill mode, the ends of lines as they appear in your text editor
are ignored. Instead, words from adjoining
are added one at a time to the output line until no more words fit.
Then, depending whether text is to be
(left, right, or centre), and depending on whether automatic
hyphenation is turned on, groff attempts to hyphenate the last word,
or, barring that, spreads and breaks the line (when justification
is turned on) or breaks and quads the line (when quadding is turned
Nofill mode (non-filled text) means that groff respects the ends
of lines as they appear in your text editor.
- Inline escapes
- Instructions issued to groff that appear as part of an
(as opposed to
which must appear on a line by themselves). Inline escapes are
always introduced by the backslash character. For example,
A line of text with the word T\*[BU 2]oronto in it
contains the inline escape \*[BU 2] (which means "move the letter
closer to the letter 'T'").
Mom's inline escapes always take the form
\*[ESCAPE], where ESCAPE
is composed of capital letters, sometimes followed immediately
by a digit, sometimes followed by a space and a
Groff's escapes begin with the backslash character
but typically have no star and are in lower case. For example, the
mom escapes to move forward 6 points on a line are
\*[FP6] or \*[FWD 6p]
while the groff escape for the same thing is
- Input line
- A line of text as it appears in your text editor.
- Instructions embedded in a document that determine how groff processes
the text for output. mom's macros always begin with a
period, on a line by themselves, and must be typed in capital letters.
Typically, macros contain complex commands issued to groff--behind
the scenes--via groff
- Machine units
- A machine unit is 1/1000 of a
when the groff device is ps. ("ps" means
"PostScript"--the default device for which groff
prepares output, and the device for which mom was
- Numeric argument
that has the form of a digit. Numeric arguments can be built out
of arithmetic expressions using +, -, *, and / for plus, minus,
times, and divided-by respectively. If a numeric argument requires
unit of measure,
a unit of measure must be appended to every digit in the
argument. For example:
NOTE: groff does not respect the order of operations,
but rather evaluates arithmetic expressions from left to right.
Parentheses must be used to circumvent this peculiarity. Not to
worry, though. The likelihood of more than just the occasional plus
or minus sign when using mom's macros is slim.
- Output line
- A line of text as it appears in output copy.
- The two-letter, lower case instructions groff uses as its
native command language, and out of which macros are built.
- String Argument
- Technically, any
that is not numeric. In this documentation, string argument means
an argument that requires the user to input text. For example, in
.TITLE "My Pulitzer Novel"
"My Pulitzer Novel" is a string argument.
Because string arguments must be enclosed by double-quotes, you can't
use double-quotes as part of the string argument. If you need
double-quotes to be part of a string argument, use the
\(lq and \(rq (leftquote and rightquote
respectively) in place of the double-quote character (").
- Unit of measure
- The single letter after a
that tells mom what measurement scale the argument
should use. Common valid units are:
|i|| = ||inches
|p|| = ||points
|P|| = ||picas
|c|| = ||centimetres
|m|| = ||ems
|n|| = ||ens
|v|| = ||the current leading (line space)|
- Units of measure must come immediately after the numeric argument (i.e.
with no space between the argument and the unit of measure), like this:
The above example advances 2 line spaces and sets the line length to
39 picas with a left indent of 1 inch.
IMPORTANT: Most mom macros
that set the size or measure of something MUST be given a unit of
measure. mom's macros do not have default units
of measure. There are a couple of exceptions, the most notable of
which are PT_SIZE and LS. Both use
as the default unit of measure, which means
you don't have to append "p" to their argument.
You can enter decimal values for any unit of measure. Different units
may be combined by adding them together (e.g. 1.5i+2m, which gives a
measure of 1-1/2 inches plus 2 ems).
NOTE: a pica is composed of 12 points,
therefore 12.5 picas is 12 picas and 6 points, not 12 picas
and 5 points. If you want 12 picas and 5 points, you have to
enter the measure as 12P+5p.
- Zero-width character
that allows you to print a literal period, apostrophe and, if
a space that falls at the beginning of an
It looks like this:
(backslash followed by an ampersand).
Normally, groff interprets a period (or an apostrophe) at the beginning
of an input line as meaning that what follows is a
In fill modes, groff treats a space at the beginning of an input
line as meaning "start a new line and put a space at the
beginning of it." If you want groff to interpret periods and
apostrophes at the beginning of input lines literally (i.e. print
them), or spaces at the beginning of input lines as just garden
variety word spaces, you must start the line with the zero-width
Mom's Document Processing Terms
- Cited material other than
Typically set at a smaller point size than paragraph text, indented
from the left and right margins. Blockquotes are
- Control macro
- Macros used in
to control/alter the appearance of document elements (e.g. heads,
- Document header/docheader
- Document information (title, subtitle, author, etc) output
at the top of page one.
- A short, usually cited passage that appears at the
beginning of a chapter, story, or other document.
- Footer/page footer
- Document information (frequently author and title) output in
the bottom margin of pages after page one. Not to be
confused with footnotes, which are considered part of
- A title that introduces a major section of a document.
- Header/page header
- Document information (frequently author and title) output in
the top margin of pages after page one.
NOTE: In terms of content and style, headers and
are the same; they differ only in their placement on the page. In
most places in this documentation, references to the content or
style of headers applies equally to footers.
- Linebreak/author linebreak
- A horizontal gap in
frequently set off by typographic symbols such as asterisks or
daggers. Used to indicate a shift in the content of a document
(e.g. a scene change in a short story). Also commonly called a
scene break or a section break.
- Paragraph head
- A title joined to the body of a paragraph; hierarchically one
- A quote, to mom, is a line-for-line setting
of quoted material (e.g. poetry, song lyrics, or a snippet of
programming code). You don't have to use
- Running text
- In a document formatted with mom, running
text means text that forms the body of the document, including
elements such as heads and subheads.
and page numbers are NOT part of running text.
- A title used to introduce secondary sections of a document;
hierarchically one level beneath sections introduced by
- A macro or tag that, when invoked without an argument,
begins something or turns a feature on, and, when invoked with
ANY argument, ends something or turns a feature off. See
of the section
How to read macro arguments.
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