Default values allow CUE to decide which element of a disjunction should be chosen when a configuration doesn’t specify a value, leaving more than one of the disjunction’s elements as valid options.

A default value is an element in a disjunction that has been prefixed with the preference marker *.

CUE will select and use the default when a value is required but none has been explicitly specified.

#def: string | int | *1

A: #def
B: #def & 42
C: #def & "foo"

$ cue export file.cue
{
    "A": 1,
    "B": 42,
    "C": "foo"
}