```
# NOT RUN {
## a class for either numeric or logical data
setClassUnion("maybeNumber", c("numeric", "logical"))
## use the union as the data part of another class
setClass("withId", contains = "maybeNumber", slots = c(id = "character"))
w1 <- new("withId", 1:10, id = "test 1")
w2 <- new("withId", sqrt(w1)%%1 < .01, id = "Perfect squares")
## add class "complex" to the union "maybeNumber"
setIs("complex", "maybeNumber")
w3 <- new("withId", complex(real = 1:10, imaginary = sqrt(1:10)))
## a class union containing the existing class union "OptionalFunction"
setClassUnion("maybeCode",
c("expression", "language", "OptionalFunction"))
is(quote(sqrt(1:10)), "maybeCode") ## TRUE
# }
# NOT RUN {
# }
```

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