Visual designer's palette

Hi All!

I’m newbie in Vaadin and my question is about visual designer plugin for eclipse.

I have task for extending ComboBox and adding to it’s class some property. This property should have ability to show itself at the VD’s palette among basic component’s properties.
Unfortunately I didn’t find any information in documentation or here, in topics, how to solve that.
While browsing sources of CustomComponent I have found that all properties are just simple class fields with private modifiers and without any anotations.
How it works?