add (REXML::Document)

    # File temp/document.rb, line 69
        def add( child )
          if child.kind_of? XMLDecl
            @children.unshift child
          elsif child.kind_of? DocType
            if @children[0].kind_of? XMLDecl
              @children[1,0] = child
            else
              @children.unshift child
            end
            child.parent = self
          else
            rv = super
            raise "attempted adding second root element to document" if @elements.size > 1
            rv
          end
        end