node.editor.top = node.editor.top + Menu_bar_height
	end

		node.editor.screen_top1, node.editor.top = schema1_of_y(node.editor, scale(Viewport.y-node.y))

		node.editor.screen_top1, node.editor.top = schema1_of_y(node.editor, scale(Viewport.y-node.y))
		node.editor.top = node.editor.top + Menu_bar_height

	-- continue the pipeline

	B(skip_updating_screen_top_for)

	B()

--? 		print('edit', old_top.line, '=>', Cursor_node.editor.screen_top1.line)
		if not eq(Cursor_node.editor.screen_top1, old_top) then
--? 			print('modifying Viewport', Viewport.y, 'based on', Cursor_node.y, Cursor_node.editor.screen_top1.line, Cursor_node.editor.line_height)
			Viewport.y = Cursor_node.y + y_of_schema1(Cursor_node.editor, Cursor_node.editor.screen_top1)/Viewport.zoom
--? 			print('modified Viewport', Viewport.y)
			-- Most of the time, we update the screen_top of nodes from Viewport.y.
			-- But here we went the other way.
			-- It's very important to avoid creating a recurrence, to avoid running
			-- both sides of this feedback loop in a single frame. These apps are
			-- not very numerically precise (e.g. we force text lines to start at
			-- integer pixels regardless of zoom, because that keeps text crisp),
			-- and the computations of Viewport.y and node.top will almost certainly
			-- not converge. The resulting bugs are extremely difficult to chase
			-- down.
			-- The optional skip_updating_screen_top_for arg ensures we don't run
			-- the other side of the feedback loop.
			A(--[[skip updating screen_top for]] Cursor_node)
			return
		end

		pan_viewport_to_contain_cursor(Cursor_node)

			pan_viewport_to_contain_cursor(Cursor_node)

compute_layout = function(node, x,y, nodes_to_render, skip_updating_screen_top_for)

compute_layout = function(node, x,y, nodes_to_render)

compute_layout = function(node, x,y, nodes_to_render)