Upper limit is returned if RegisterCopyAttributeWithUpperLimit is performed with default value as source value. See: https://github.com/stefan-lindegger/BBT.StructureTools/blob/495c47f0369a30b15f5f4051e682fca6930f4db2/src/BBT.StructureTools/Provider/DefaultValueProvider.cs#L29 and https://github.com/stefan-lindegger/BBT.StructureTools/blob/495c47f0369a30b15f5f4051e682fca6930f4db2/src/BBT.StructureTools.Tests/Convert/ConverterIntTests.cs#L340