@Section
   @Title { Displays }
   @Tag { displays }
@Begin
@PP
The @Code "@Display" symbol displays the following object in the centre
displays. @Index displays
display. @Index @Code "@Display"
of the page or column:
@ID @Code "@Display @I { Invitation to Afternoon Tea }"
has result
@Display @I { Invitation to Afternoon Tea }
Space is inserted automatically above and below the display; no
paragraph symbols are needed.
@PP
To display at the left margin instead of centred, use
leftdisplay. @Index @Code "@LeftDisplay"
{@Code "@LeftDisplay"} instead of {@Code "@Display"}.  To indent
the display, use {@Code "@IndentedDisplay"} or {@Code "@QuotedDisplay"};
indenteddisplay. @Index @Code "@IndentedDisplay"
quoteddisplay. @Index @Code "@QuotedDisplay"
the latter indents at the right margin as well as at the left. There are
also @Code "@CentredDisplay" and @Code "@CenteredDisplay" symbols which
centreddisplay. @Index @Code "@CentredDisplay"
centereddisplay. @Index @Code "@CenteredDisplay"
centre the display (like {@Code "@Display"}), and
rightdisplay. @Index @Code "@RightDisplay"
@Code "@RightDisplay" which right-justifies the display.
@PP
If you use displays frequently you might prefer abbreviated forms of
their names.  These are made from @Code "@" and the capital letters of
d. @Index @Code "@D"
ld. @Index @Code "@LD"
id. @Index @Code "@ID"
qd. @Index @Code "@QD"
cd. @Index @Code "@CD"
the full name:  {@Code "@D"}, {@Code "@LD"}, {@Code "@ID"}, {@Code "@QD"},
and {@Code "@CD"}.  Owing to a clash with the name of another symbol,
{@Code "@RightDisplay"} has no abbreviation.
@PP
Displays often need to be set using a different font, paragraph
breaking style, and so on to the surrounding text.  It's best to set
out such displays like this:
@ID @OneRow @Code {
"@CentredDisplay @I clines @Break {"
"Invitation to Afternoon Tea"
"with"
"Mr. and Mrs. Gilbert Newington-Smith"
"}"
}
You can have as many of these symbols as you like, including specialized
ones like {@Code "@CurveBox"} and {@Code "@Tbl"}.  The only rule is that
the display symbol must come first:  @Code "@I @Display ..." is wrong.
@PP
It's not a good idea to have one display immediately followed by
another one, because there will be too much vertical space between
them.  Use a list instead (Section {@NumberOf lists}).  Displays
at the ends of paragraphs look awkward and are best avoided.
@PP
A display may come out partly on one page or column and partly on
the next, if it has places where it obviously can be broken in two.  For
example, a display which is an ordinary paragraph of text might be
broken in two between any two lines.  To force a display to keep
together on one page or column, use the @Code "@OneRow" symbol like
this:  @Code "@Display @OneRow { ... }".
@PP
Other display symbols produce aligned and numbered displays, and raw
displays (i.e.  without vertical space).  Although these can display any
object as usual, in practice they are used for mathematics, so they are
described in Section {@NumberOf mathdisplays}.
@PP
Three setup file options control the appearance of displays.  (For a
general introduction to setup files and their options, consult
Section {@NumberOf setup}.)  Here they are with their default values:
@ID @OneRow @Code {
"@DisplayGap { 1.00v }"
"@DefaultIndent { 0.5rt }"
"@DisplayIndent { 2.00f }"
}
@Code "@DisplayGap" is the amount of vertical space inserted before and
display.gap. @Index @Code "@DisplayGap"
after displays, and may be any length (Section {@NumberOf objects}).  The
default value, @Code {"1.00v"}, is equal to the current inter-line spacing.
@PP
@Code "@DefaultIndent" is the indent produced by
default.indent @Index @Code "@DefaultIndent"
{@Code "@Display"}; {@Code "0.5rt"} produces centring, although why it does
so is beyond our scope
@Cite { $kingston1995lout.expert }.  @Code "@DisplayIndent" is the
display.indent. @Index @Code "@DisplayIndent"
indent for {@Code "@IndentedDisplay"}, and (at both margins) for
{@Code "@QuotedDisplay"}.  Its default value, {@Code "2.00f"}, is twice
the current font size.
@End @Section
