[R] Highlight overlapping area between two curves

[Nguyen Dinh Nguyen]

Dear R helpers,
I have a graph as following; I would like to highlight the overlapping area
between the two curves. Do you know how to do this?
Thank you in advance for your help.
Nguyen

###START
x1 <- rnorm(10000, 0.70,0.12)
x2 <- rnorm(10000, 0.90,0.12)

d1 <- density(x1)
d2 <- density(x2)

plot(range(d1$x,d2$x), range(d1$y, d2$y), type = "n",
     xlab = "X value", ylab = "Probability Density" )

lines(d1, col = "red",lwd=4, lty=2)
lines(d2, col = "blue",lwd=4)

##END CODE