         _ -> nil
       end)
     case maybe_var do
-      nil -> "[UNKNOWN #{var}]"
+      nil -> :unknown_var
       {_k, v} -> v
     end
   end

    {:ok, res}
  end

  def re_find_and_replace("", context) do # nice for debugging: {{}}
    inspect context
  end

    case res do
      txt when is_binary(txt) -> txt
      num when is_number(num) -> to_string(num)
      :unknown_var -> "{{#{var}}}"
      other -> inspect other
    end
  end

  def re_find_and_replace_leaf(var, nil) do
    :unknown_var
  end
  def re_find_and_replace_leaf(var, :unknown_var) do
    :unknown_var
  end
  def re_find_and_replace_leaf(_var, s) when is_binary(s) do
    s
