A field name that starts with an underscore (_) is referred to as a hidden field. Hidden fields are not included in the exported output.

If a field’s name is enclosed in quotes then it is not hidden from exported output - even if it starts with an underscore. To output a field whose name starts with an underscore, enclose its name in quotes.

Quoted and non-quoted fields share the same namespace unless they start with an underscore.

foo: int & <100 // This is a regular field.

// This is the same regular field as above, so
// both their values must unify successfully.
"foo": 1

// These two declarations refer to different
// fields, only one of which will be included in
// exported output.
_foo:   2
"_foo": 3

// This is a hidden definition, which is not
// included in exported output.
_#foo: 4

$ cue export file.cue
{
    "foo": 1,
    "_foo": 3
}