Adding properties at design time

Hi, I''m looking resources or tutorial where I can learn how to add properties to other objects at design time. I want to reproduce the same effect as when your drop the tooltip object on a form. Once it''s done, every object has a new property added to the property box so we can write the tooltip text. Syncfusion object does something like that when we drop a docking manager tool. It adds 3 new properties to every object that can use this resources. I tried to find information but maybe because I don''t know how to call that effect, I was not succesfull to find information. Thank you very much. Miky