Unit to use for prettier printing of role values in a browser. Useful values are:"<unitName>" as a string. Shorthand for the following LIST:
'(:unit <unitString> [<precision>]) for output in a particular unit with optional
precision (number of decimal places).
'(:best-fit <unitString1> ... <unitStringN> [precision]) for output with the unit that
best fits the value from the
given choices. Precision as above.
'(:step <unitString1> ... <unitStringN> [precision]) for output with multiple units, where
the largest units have integer values
and smaller units are used for the remainder. The optional precision
argument is applied only to the smallest unit actually used.
** Note that this format cannot be read back in **
(=> (Output-Unit ?A ?B) (Or (String ?B) (Symbol ?B)))