public enum SelectionCombinationMethod : System.Enum, System.IComparable, System.IConvertible, System.IFormattable, System.ISpanFormattable  

{
    var options = ApplicationOptions.SelectionOptions;
    //Note: Run within a QueuedTask
    var defaultColor = options.DefaultSelectionColor;
    //Set the selection color to red
    var color = options.SelectionColor as CIMRGBColor;
    options.SetSelectionColor(ColorFactory.Instance.CreateRGBColor(255, 0, 0));

    //Set the selection fill color and fill hatch
    var defaultFill = options.DefaultSelectionFillColor;
    var fill = options.SelectionFillColor;
    var isHatched = options.IsSelectionFillHatched;
    options.SetSelectionFillColor(ColorFactory.Instance.CreateRGBColor(100, 100, 0));
    if (!isHatched)
        options.SetSelectionFillIsHatched(true);
    //Toggle the selection Chip and Graphic
    var showSelectionChip = options.ShowSelectionChip;
    options.SetShowSelectionChip(!showSelectionChip);

    var showSelectionGraphic = options.ShowSelectionGraphic;
    options.SetShowSelectionGraphic(!showSelectionGraphic);

    //Get the value indicating whether to save the layer and standalone table selection with the map.
    var saveSelection = options.SaveSelection;
    options.SetSaveSelection(!saveSelection);
    //Get/Set the selection tolerance
    var defaultTol = options.DefaultSelectionTolerance;
    var tol = options.SelectionTolerance;
    options.SetSelectionTolerance(2 * defaultTol);

    // extension methods available for selection methods and combination methods
    var selMethod = options.SelectionMethod;
    options.SetSelectionMethod(SelectionMethod.Contains);

    var combMethod = options.CombinationMethod;
    options.SetCombinationMethod(SelectionCombinationMethod.Add);

    // note that the following SelectionCombinationMethod is not supported
    //options.SetCombinationMethod(SelectionCombinationMethod.XOR);
}

//Map Tool is used to perform Spatial selection.
//Graphic selection uses the selection geometry 
//to intersect the geometries of those elements (graphic or group) 
//that will be selected and then highlights them. 
{
  var selPoly = geometry as Polygon;
  // Note: must be called on the QueuedTask
  {
    //note: the selected elements may belong to more than one layer...
    var elems = MapView.Active.SelectElements(selPoly, SelectionCombinationMethod.New);
  }
}

{
  // Note: must be called on the QueuedTask
  {
    //Create an extent to use for the spatial selection
    var extent = MapView.Active.Extent;
    var selectionExtent = extent.Expand(0.5, 0.5, true);
    //Select elements in specified graphics layer using the selection extent.
    var selectedElements = MapView.Active.SelectElements(graphicsLayer, selectionExtent, SelectionCombinationMethod.Add);
  }
}

{
  var all_text = graphicsLayer.GetElementsAsFlattenedList()
                .Where(e => e.GetGraphic() is CIMTextGraphic);
}