anchor.diff:              (dict : ObservableDictionaryBase<obj, obj>, keys : NonNull<obj> array) =
           // The generator doesn't generate empty dictionaries, which can throw
           // off the isAddition/isReplace logic
  -        dict.Clear ()
  +        //dict.Clear ()
   
           // Add event tracker *after* the preprocessing
           let counts = Observer dict
  
positive.code:             .&. isZeroProperty "no unrecognized property events"     counts.UnrecognizedPropertyChanges
          )
  
  type Keys =
      //TODO: This doesn't check replacing values
      [<Property>]
  
negative.code: open System.Collections.Specialized
  open System.ComponentModel
  
  open Xunit
  open FsCheck
  open FsCheck.Xunit
  
  