Specifying a field multiple times with conflicting values results in an error, or bottom, written _|_.

Bottom is a special value in CUE, and is the value that results from any error. Logically, all errors are equal, although CUE may associate them with metadata such as an error message.

An error is not the same as the value null. _|_ isn’t a valid value for a field, but null is.

a: 1
a: 2

b: [50, 100]
b: [50, 200]

c: [0, 1, 2]

d: c[5]
$ cue eval -i file.cue
a: _|_ // a: conflicting values 2 and 1
b: [50, _|_, // b.1: conflicting values 200 and 100
c: [0, 1, 2]
d: _|_ // d: invalid list index 5 (out of bounds)

Notice how the -i flag changes how cue eval behaves. It causes errors to be represented as literal error values in the output, with error messages as inline comments. These literal _|_ values invalidate the CUE that’s output.