elseif string.match(column_name, '%S+ from %S+') then
    local rel, start_id = string.match(column_name, '(%S+) from (%S+)')
    initialize_cache_if_necessary(start_id)
    local column = unroll_column(start_id, rel)
    if column == nil then
      -- something has changed from underneath us
      -- unroll_column printed out an error

  else
    -- helpers that create columns you have to explicitly insert
    local column = {name=column_name}
    populate_column(column)
    if #column == 0 then
      -- Something has changed from underneath us, likely between restarts;
      -- assume we already printed out an error.

  elseif string.match(column_name, 'neighbors of %S+') then
    local start_id = string.match(column_name, 'neighbors of (%S+)')

  end
end
function populate_column(column)
  if string.match(column.name, '%S+ from %S+') then
    local rel, start_id = string.match(column.name, '(%S+) from (%S+)')

    local column = {name=('neighbors of %s'):format(start_id)}
    table.insert(column, load_pane_from_file(start_id))
    for rel,target in pairs(Cache[start_id].links) do
      table.insert(column, load_pane_from_file(target))
    end
    table.insert(Surface, column)

    populate_unroll_column(column, start_id, rel)
  elseif string.match(column.name, 'neighbors of %S+') then
    local start_id = string.match(column.name, 'neighbors of (%S+)')
    initialize_cache_if_necessary(start_id)
    populate_neighbors_column(column, start_id)
  else
    error("don't know how to populate column \""..column.name.."\"")

  local column = unroll_column(pane.id, rel)
  if column == nil then

  local column = {name=('%s from %s'):format(rel, pane.id)}
  populate_unroll_column(column, pane.id, rel)
  if #column == 0 then

function unroll_column(id, rel)

function populate_unroll_column(column, id, rel)
  -- back out to start of chain

  local column = {name=('%s from %s'):format(rel, id)}

  -- unroll from start

  return column

  table.insert(column, load_pane_from_file(pane.id))
  for rel,target in pairs(Cache[pane.id].links) do
    table.insert(column, load_pane_from_file(target))
  end

  populate_neighbors_column(column, pane.id)

function populate_neighbors_column(column, start_id)
  table.insert(column, load_pane_from_file(start_id))
  for rel,target in pairs(Cache[start_id].links) do
    table.insert(column, load_pane_from_file(target))
  end
end