def header=(header)
         if header.type == HeaderNode::UNIVERSAL
            @headers[0] = header
         elsif header.type == HeaderNode::LEFT_PAGE
            @headers[1] = header
         elsif header.type == HeaderNode::RIGHT_PAGE
            @headers[2] = header
         elsif header.type == HeaderNode::FIRST_PAGE
            @headers[3] = header
         end
      end
def header=(header)
         if header.type == HeaderNode::UNIVERSAL
            @headers[0] = header
         elsif header.type == HeaderNode::LEFT_PAGE
            @headers[1] = header
         elsif header.type == HeaderNode::RIGHT_PAGE
            @headers[2] = header
         elsif header.type == HeaderNode::FIRST_PAGE
            @headers[3] = header
         end
      end
This method assigns a new header to a document. A Document object can
 have up to four header - a default header, a header for left pages, a
 header for right pages and a header for the first page. The method
 checks the header type and stores it appropriately.

 ==== Parameters
 header::  A reference to the header object to be stored. Existing header
           objects are overwritten.