code: def header(type=HeaderNode::UNIVERSAL)
           index = 0
           if type == HeaderNode::LEFT_PAGE
              index = 1
           elsif type == HeaderNode::RIGHT_PAGE
              index = 2
           elsif type == HeaderNode::FIRST_PAGE
              index = 3
           end
           @headers[index]
        end
docs: This method fetches a header from a Document object.
  
   ==== Parameters
   type::  One of the header types defined in the header class. Defaults to
           HeaderNode::UNIVERSAL.