When you define a public property in a class and it has a visualization (eg.Form/UserControl), this property will be displayed in the Properties view, but only if it is a primitive datatype. If it is of an objecttype, based on a class you have built yourself; it will not show in the Properties view.
For example: I have a public property Dimension in a usercontrol. This is based on the Dimension class which has itself 3 public properties: X, Y and Z, all integers. I would like this to be displayed in the Properties view, comparable to display in the Properties view of the System.Drawing.Point class.