Using Onlyif but dependant on the parent viewmodel?

We have a parent/child viewmodel set up so that a parent record can have multiple child records. We need a validation rule on the child record that is only required when a field on the parent has a certain value.

Is this possible?
I've tried this in the child viewmodel:
` required: {
onlyIf: function () {
return parent.FieldX() == Value;
}
}
`
Where `parent` is the `self` variable passed from the parent viewmodel to the child viewmodel. No errors generated, but this still doesn't work.

Start by tracing the `onlyIf` validation option from the child viewmodel example and reproduce the parent/child setup described in the issue. Check how the condition is evaluated when it references the parent viewmodel, then define completion as a confirmed supported behavior or a documented, tested correction for the reported case.

Written by the indexing model from the issue text.