The attached properties are a special kind of properties. They are defined on one control but actually affect another control. While this might sound a bit confusing, the truth is we have actually used attached properties all along without knowing what they really are. The attached properties can be recognized quite easily as they have a constant syntax of PropertyTypeName.AttachedPropertyName. Think about the Grid.Row property for example, or Grid.Column. In these cases, Grid is the type and the property we are setting for it is either Row or Column. The element, which we define this property on, TextBox, or any other UI Element, doesn't have a Grid.Row property. In fact, it doesn't even know if it's placed inside Grid, Canvas, StackPanel, or any other layout control. Instead, the Grid.Row property tells the parent Grid element in which row to place the calling object. If we take TextBox, which resides inside Grid, and set its Grid.Row property to 3...