def valid_parent_types(child)
      # could be a node object, or maybe a string
      str = child.respond_to?(:entity_type) ? child.entity_type : child
      self.up_taxonomy[str]
    end
def valid_parent_types(child)
      # could be a node object, or maybe a string
      str = child.respond_to?(:entity_type) ? child.entity_type : child
      self.up_taxonomy[str]
    end
access the appropriate parent entity_types for a particular child or child entity_type
 @param [Taxonomy::Node, String] child the child object or entity_type string
 @return [Array] an array of strings which are the valid parent types for the child