```
if (FALSE) {
library(xts)
data(sample_matrix)
x <- as.xts(sample_matrix)[,1]
ix <- index(x["2007-02"])
shade <- xts(matrix(rep(range(x), each = length(ix)), ncol = 2), ix)
plot(x)
# set on = -1 to draw the shaded region *behind* the main series
addPolygon(shade, on = -1, col = "lightgrey")
}
```

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