In some cases, attributes in railML® are defined by physical units. All employed units are listed in Category:Unit. A historic overview regarding railML® 2.x can be found here.
Generally the attributes are defined via SI units (). But there are exceptions for well established non-SI units. E.g. in <diesel> (railML® 2), the fuelCapacity of a diesel engine is expressed in litres rather than cubic meters.
||As a wiki editor, please allways employ Template:Unit to define attribute types characterized by physical units or any established nonphysical units.