def parent_name( key )
      return if :root == key

      a = key.split PATH_DELIMITER
      p = :root
      while a.slice!(-1) and !a.empty?
        k = a.join PATH_DELIMITER
        if @h.has_key? k then p = k; break end
      end
      p
    end
def parent_name( key )
      return if :root == key

      a = key.split PATH_DELIMITER
      p = :root
      while a.slice!(-1) and !a.empty?
        k = a.join PATH_DELIMITER
        if @h.has_key? k then p = k; break end
      end
      p
    end
Returns the name of the parent for the logger identified by the given
 _key_. If the _key_ is for the root logger, then +nil+ is returned.