The expression `0.2e+2_2-2e-2` for example results in `2e+21` in the Python console, but when entered in the transform system evaluates to 399.98.
eg:
```
>>> 2e+2-2e-2-2e+2
-0.020000000000010232
>>> bpy.utils.units.to_value('METRIC', 'LENGTH', '2e+2-2e-2-2e+2')
399.98
```
In 2.82 these give the same output.