| activeOptionsIndices | A Span of type integers with the allocated size to hold the number of active indices. | 
Retrieves a Span of integers containing the active options as indices.
 public void HandleActiveOptions()
 {
     var value = myToggleButtonGroup.value;
     var options = value.GetActiveOptions(stackalloc int[value.length]);
     foreach (option in options)
     {
         // handle option
     }
 }