Correct way to define AlternateUnit or alias of same unit

[laeubi]

I tried to use AlternateUnit for example AlternateUnit.of(MetricPrefix.NANO(Units.METRE), "nm", "Wavelength");
but this throws IllegalArgumentException: The parent unit: nm is not an unscaled SI unit.

Next attempt something like AlternateUnit.of(METRE, "λ", "Wavelength") + NANO(...) produces symbol nλ instead of nm, I think one can workaround this by mapping it to an own symbol.

What somehow worked was new TransformedUnit<>("nm", "Wavelength", Units.METRE, MultiplyConverter.ofRational(1, 1_000_000_000L)); but must manually duplicate the conversion factor that MetricPrefix.NANO(METRE) already defines.

A similar problem arise for example if one want to have a Distance in km to be distinguishable from a Length in km, so my question is what is the "standard way" to archive such kind of "alias" of a unit?

I find it sometimes hard to get how to use the API for such cases, is there some official documentation that describes all the differences between when to use BaseUnit / AlternateUnit / TransformedUnit / ... ?