returns default if distance can't be calculated. unit1 and unit2 may be unit tables with .coordX etc members, or unit designators suitable for Inspect.Unit.Detail.
x = nf.prettydistance(unit1, unit2, default)
Yields a string value.
x = nf.prettydistance(numeric)
Same string value.
Added range/prettyrange which subtract unit radius, since that's what spells use.
Note: I can't find a way to detect whether or not two units have comparable coordinates. Say, dimensions, instances, and such. You could check whether units are in instances, but since you can have different zone IDs outside of instances, it may be that you can have different zone IDs within a given instance...
0.2: range (less radii of units) added
0.3: TOC updates
0.4: ToC updates.