Hmisc interaction behavior

Dear R-helpers,

Can someone explain to me why the function interaction() from the Hmisc library results in numeric?

test1 <- c("A","B","C")
test2 <- c("D","E","F")

is.numeric(interaction(test1,test2))

[1] TRUE

I had problems with this side effect in a different function.

thanks,

Remko Duursma