问fancyRpartPlot决策树中节点顶部的数字是什么意思？

EN

> dt <- rpart::rpart(Species ~ ., iris)
> print(dt)
n= 150 

node), split, n, loss, yval, (yprob)
      * denotes terminal node

1) root 150 100 setosa (0.33 0.33 0.33)  
  2) Petal.Length< 2.45 50   0 setosa (1.00 0.00 0.00) *
  3) Petal.Length>=2.45 100  50 versicolor (0.00 0.50 0.50)  
    6) Petal.Width< 1.75 54   5 versicolor (0.00 0.91 0.093) *
    7) Petal.Width>=1.75 46   1 virginica (0.00 0.022 0.98) *
> rattle::fancyRpartPlot(dt)

  if(nn || ni)
        draw.node.numbers(nn, ni, draw.shadows1, type, branch,
                Margin, xflip, yflip, cex,
                main, sub, col.main, cex.main, col.sub, cex.sub,
                xlim, ylim, node.xy, is.leaf, nodes,
                node.labs, font,  family, box.col, border.col, shadow.col,
                under.cex, under.font, under.ygap, ygap,
                split.labs, split.cex * cex, split.font, split.family, split.box.col,
                split.border.col, split.shadow.col,
                nn.cex, nn.font, nn.family, nn.col, nn.box.col,
                nn.border.col, nn.lty, nn.lwd, nn.round,
                split.adj, split.space, split.yspace, split.yshift,
                yshift, adj, space, yspace, shadow.offset,
                nn.adj, nn.yshift, nn.space, nn.yspace, bg)

list(node.boxes=node.boxes, split.boxes=split.boxes)