-- a.cue --
@layer(2,defaultData)
mixed: {
	fromData: 1
	fromBoth: 2
}
-- b.cue --
@layer(3)
mixed: {
	fromNormal: 10
	fromBoth: 20
}
-- out/layer --
mixed.fromBoth: conflicting values 20 and 2:
    ./a.cue:4:12
    ./b.cue:4:12
