Negative values are permitted. A negative value places the origin of the element where Canvas.Top is applied off-screen to the top side of the content area.
This property is an example of an attached property, whereby non-Canvas objects can set this property that can then be read and interpreted by a parent Canvas.
The value is interpreted by any immediate parent Canvas. If there are nested canvas elements, values for Canvas.Top that do not come from immediate child elements are ignored. A Canvas can itself have a Canvas.Top value, but the value does not apply on itself, rather it is interpreted by any parent Canvas, as in the nested scenario mentioned.