CUE allows fields to be specified multiple times, so long as all the values don’t conflict. If the values don’t conflict we say they unify successfully. Unification is the process of checking that values don’t conflict, and it happens implicitly whenever any field is redeclared.

For concrete data, unification of basic types requires that all values specified for a field must be equal.
Within structs, fields are unified recursively. Similarly, within lists, elements are unified recursively.

A: 1
A: 1

B: {a: 2}
B: {b: 3}

C: [4, 5, {c: 6}]
C: [4, 5, {d: 7}]

$ cue export file.cue --out yaml
A: 1
B:
  a: 2
  b: 3
C:
  - 4
  - 5
  - c: 6
    d: 7