I guess, it depends on how complex or simple the structure is.
I will make x and y as attribute, unless x and y have their own details
You can look at HTML or any other form of markup, which is used to define things (XAML in case of WPF, MXML in case of flash) to understand, why something is chosen as attribute as against a child node)
if x and y are not to be repeated, they can be attributes.
Lets say co-ordinates has multiple x and y, I guess xml doesnt allow multiple attributes with same name for a node. In that case, you will have to use child nodes.
