@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, so no
paragraph symbols are needed anywhere near it.
@PP
To make the display appear at the left margin instead of centred, use
leftdisplay. @Index @Code "@LeftDisplay"
{@Code "@LeftDisplay"} instead of {@Code "@Display"}.  To make an indented
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 just like {@Code "@Display"} does, 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 an unfortunate clash with the name of
another symbol, there is no abbreviation for {@Code "@RightDisplay"}.
@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 symbols like {@Code "@CurveBox"}, {@Code "@Eq"}, and
{@Code "@Tab"}.  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
There are other display symbols for producing more advanced kinds
of displays:  aligned and numbered displays, and raw displays (i.e.
without vertical space).  Although these symbols can display any
object as usual, in practice they are used for displaying mathematics,
so they are described in Section {@NumberOf mathdisplays}.
@PP
Three setup file options are provided for controlling 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"}; the default value, {@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 produced by {@Code "@IndentedDisplay"}, and at both margins by
{@Code "@QuotedDisplay"}.  Its default value, {@Code "2.00f"}, is twice
the current font size.
@End @Section
