Table Widget / Perform expression on datapoint

Yeah, nothing built-in for that. Normally I would either put in note in the title of the widget or the column (like "0=offline") or have a text widget explaining specific columns and codes.

Another trick I use is the column's color bars so it makes it a bit more obvious. For example if 0=offline and 1=online, I would set the color bars for that column to have Red when current value is =0 and fiddle with the min/max values so it fills in the whole cell.