# File nqxml/treeparser.rb, line 43
 def handleTagStart(entity)
	    parent = @nodeStack.last
	    node = Node.new(entity, parent)

	    if parent.nil?
		# If parent is nil, we are at top level.
		if !@document.rootNode.nil?
		    str = "tag '#{entity.name}' seen after close of" +
			' top-level tag; there can only be one top-level tag'
		    raise ParserError.new(str, @tokenizer)
		end
		@document.setRootNode(node)
	    else
		parent.children << node
	    end

	    @nodeStack.push(node)
	end