> # Unknown names
> select_loc(mtcars, foobar & contains("am"))
Error: Can't subset columns that don't exist.
x The column `foobar` doesn't exist.

> select_loc(mtcars, contains("am") | foobar)
Error: Can't subset columns that don't exist.
x The column `foobar` doesn't exist.

> # Empty intersection
> select_loc(mtcars, cyl & am)
Error: Can't take the intersection of two columns.
i `cyl & am` is always an empty selection.

> # Symbol operands are evaluated in strict mode
> foo <- 1:2
> select_loc(iris, Species | foo)
Error: Can't subset columns that don't exist.
x The column `foo` doesn't exist.

