Proposed Syntax

{ <path>: $_internalSchemaObjectMatch: {
        <ObjectConstraintMatchExpression>,
        <ObjectConstraintMatchExpression>,
        ...
    }
}

Proposed Semantics

The field at <path> matches the expression if it is an object and matches the sub-expression <topLevelMatchExpression>. $_internalSchemaObjectMatch allows for constraining the properties of a nested object, as top-level match expressions on their own cannot be used to constrain a subobject.