box_height = function(node)
	-- return the height of a node. The result is scaled.
	print('computing box height based on font size', node.scaled_fontsize, node.editor.font_height, node.editor.line_height)
	if #node.editor.lines > 1 then Box_heights = {} end
  local y = 0
  for i=1,#node.editor.lines do
    local line = node.editor.lines[i]
    if node.editor.line_cache[i] == nil then
      node.editor.line_cache[i] = {}
    end
    node.editor.line_cache[i].fragments = nil
    node.editor.line_cache[i].screen_line_starting_pos = nil
    Text.compute_fragments(node.editor, i)
    Text.populate_screen_line_starting_pos(node.editor, i)
    y = y + node.editor.line_height*#node.editor.line_cache[i].screen_line_starting_pos
	if #node.editor.lines > 1 then
		table.insert(Box_heights, y)
	end
    Text.clear_screen_line_cache(node.editor, i)
  end
  return y
end