Working through building out schema models.

Perhaps the most complex model in the stack, almost there! a small amount of refactoring also to help things stay clean.

datamodel/low/reference.go

@@ -21,3 +21,7 @@ type ObjectReference struct {
 	ValueNode *yaml.Node
 	KeyNode   *yaml.Node
 }
+
+func (n NodeReference[T]) IsEmpty() bool {
+	return n.KeyNode == nil && n.ValueNode == nil
+}