The DESIGN-time name of a sheet. A sheet's name and the name of one INSTANCE of that sheet are different things which have had the same type - bare string - for as long as the waveform simulator has existed. That is why SimTypes and ModelType each carry a long comment warning about the confusion, and why FastCreate needs a collision hack for it. Wrapping the design-time one is half of telling them apart; SimSheetId below is the other half. Wrapped at the simulator interface only. It is deliberately NOT pushed into LoadedComponent.Name, CustomComponentType.Name or SimpleSheet.SheetName: those cross the .dgm persistence boundary and the SimpleJsonDotNet wire boundary, and [] does not mean the same thing under Fable as under .NET.