Recently ndigits was changed to have an "all" and "pdg" mode. An alternative was to have these two options be on round_mode, I think this latter would be more natural. I chose the former in anticipation of the resolution to #177 where I thought users might specify a fallback_ndigits to use for the value when the uncertainty is invalid. Doing it this way gives users a little more control on the fallback. But I realized users could have FULL control over the fallback if they just provide an additional formatter. This pollutes the option space even less in my opinion. Because of this I think the all and pdg options should be moved into round_mode with ndigits always being an integer and only used in sig_fig and dec_place modes.