def target_named(target_name)
      return target_name if target_name.is_a?(Epuber::Book::Target)

      flat_all_targets.find do |target|
        target.name == target_name || target.name.to_s == target_name.to_s
      end
    end
def target_named(target_name)
      return target_name if target_name.is_a?(Epuber::Book::Target)

      flat_all_targets.find do |target|
        target.name == target_name || target.name.to_s == target_name.to_s
      end
    end
--------------------------------------------------------------------- 
 @!group Other methods
 Finds target with name or nil when not found

 @param target_name [Symbol, String, Epuber::Book::Target]

 @return [Epuber::Book::Target, nil]