How to add more data to tooltip in R plotly (besides the `text` argument)

General
2 
library(plotly)

x <- y <- 0:100
z <- outer(X = x, Y = y, function(x, y) 2*x + 3*y)
# sum <- outer(X = x, Y = y, function(x, y) x + y)
# product <- outer(X = x, Y = y, function(x, y) x * y)
# difference <- outer(X = x, Y = y, function(x, y) x - y)

txt <- as.character(outer(X = x, Y = y, function(x, y) 
  glue::glue("sum is {x+y}<br>product is {x*y}<br>difference is {x-y}")))

plot_ly(
  type = "contour",
  x = x,
  y = y,
  z = z,
  text = txt,
  hovertemplate = "x is %{x}<br>y is %{y}<br>z is %{z}<br>%{text}<extra></extra>"
)

image