# A XML representation of the AST
	# Productions and token become elements
	# 
	# detached tokens and whitespaces are preserved in the XML
	# 
	# ~~~
	# import parser_util
	# var text = "y += foo"
	# var ast = (new ToolContext).parse_something(text)
	# assert ast isa AExpr
	# ast.parentize_tokens
	# assert ast.to_xml.write_to_string == """<ACallReassignExpr><AQid><TId>y</TId></AQid> <APlusAssignOp><TPluseq>+=</TPluseq></APlusAssignOp> <ACallExpr><AQid><TId>foo</TId></AQid></ACallExpr></ACallReassignExpr>"""
	# ~~~
	fun to_xml: HTMLTag
	do
		var res = new HTMLTag("AST")
		var stack = new Array[HTMLTag]
		var c = first_token
		while c != null do
			if c != first_token then res.append(c.blank_before)
			var sp = c.starting_prods
			if sp != null then for p in sp do
				var tag = new HTMLTag(p.class_name)
				res.add tag
				stack.add res
				res = tag
			end
			var tag = new HTMLTag(c.class_name)
			res.add tag
			tag.append c.text
			var ep = c.ending_prods
			if ep != null then for p in ep do
				res = stack.pop
			end

			if c == last_token then
				c = null
			else
				c = c.next_token
			end
		end
		assert stack.is_empty
		return res.children.first
	end