@Section
   @Title { Adding a key to the graph }
   @Tag { key }
@Begin
@PP
A @I key to a graph is an explanation of what each data set
key. @Index { key in graph }
represents.  To assist you in constructing a key, some extra symbols
are provided in addition to {@Code "@Graph"}:
graph.cross @Index @Code "@GraphCross"
graph.plus @Index @Code "@GraphPlus"
graph.square @Index @Code "@GraphSquare"
graph.filled.square @Index @Code "@GraphFilledSquare"
graph.diamond @Index @Code "@GraphDiamond"
graph.filled.diamond @Index @Code "@GraphFilledDiamond"
graph.circle @Index @Code "@GraphCircle"
graph.filled.circle @Index @Code "@GraphFilledCircle"
graph.triangle @Index @Code "@GraphTriangle"
graph.filled.triangle @Index @Code "@GraphFilledTriangle"
graph.noline @Index @Code "@GraphNoLine"
graph.solid @Index @Code "@GraphSolid"
graph.dashed @Index @Code "@GraphDashed"
graph.dotted @Index @Code "@GraphDotted"
@ID @Tab
    @Fmta { @Col @Code A ! @Col B ! @Col @Code C ! @Col D }
{
@Rowa
    A { "@GraphCross" }
    B { @GraphCross }
    C { "@GraphPlus" }
    D { @GraphPlus }
@Rowa
    A { "@GraphSquare" }
    B { @GraphSquare }
    C { "@GraphFilledSquare" }
    D { @GraphFilledSquare }
@Rowa
    A { "@GraphDiamond" }
    B { @GraphDiamond }
    C { "@GraphFilledDiamond" }
    D { @GraphFilledDiamond }
@Rowa
    A { "@GraphCircle" }
    B { @GraphCircle }
    C { "@GraphFilledCircle" }
    D { @GraphFilledCircle }
@Rowa
    A { "@GraphTriangle" }
    B { @GraphTriangle }
    C { "@GraphFilledTriangle" }
    D { @GraphFilledTriangle }
@Rowa
@Rowa
    A { "@GraphNoLine" }
    B { @GraphNoLine }
@Rowa
    A { "@GraphSolid" }
    B { @GraphSolid }
@Rowa
    A { "@GraphDashed" }
    B { @GraphDashed }
@Rowa
    A { "@GraphDotted" }
    B { @GraphDotted }
}
These extra symbols may be used anywhere in your document except within
the right parameter of {@Code "@Graph"}; they are commonly used within
the caption options of {@Code "@Graph"}:
@ID @OneRow @Code {
"@Graph"
"    rightcaption {"
"@GraphPlus @GraphSolid @GraphPlus  Boston"
"@GraphPlus @GraphDashed @GraphPlus  New York"
"@GraphPlus @GraphDotted @GraphPlus  Philadelphia"
"}"
}
Recall that unlike the other captions, @Code rightcaption is set using
the @Code "lines @Break" style rather than {@Code "clines @Break"}
(Section {@NumberOf captions}).  Adding this caption to the graph
from Section {@NumberOf data}, the complete result is
@CD @Graph
    rightcaption {
@GraphPlus @GraphSolid @GraphPlus  Boston
@GraphPlus @GraphDashed @GraphPlus  New York
@GraphPlus @GraphDotted @GraphPlus  Philadelphia
}
{
    @Data  points { plus }  pairs { solid }
    { 1720 12000  1730 13000  1740 15601  1760 15631  1770 15877 }

    @Data  points { plus }  pairs { dashed }
    { 1720 7000  1730 8622  1740 10451  1750 14255  1760 18000  1770 22667 }

    @Data  points { plus }  pairs { dotted }
    { 1720 10000  1730 11500  1740 12654  1750 18202  1760 23750  1770 34583 }

}
The first eight symbols have a @Code "symbolsize" option with the
usual meaning and the usual default value ({@Code "0.15 ft"}).  The
last four symbols have @Code "dashlength" and @Code "linewidth" options
with the usual default values, {@Code "0.2 ft"} and {@Code "0.5 pt"}
respectively, and a @Code "length" option, which determines the length
of the line drawn by each symbol; its default value is {@Code "1.0 ft"}.
@End @Section
