Cross UI Extensions communication

Hi all! Lets say I have two custom ui extensions. The first one works with FieldExtensionSDK and the second one with SidebarExtensionSDK. How can I communicate between them? I expect to have something like sdk.entry.onChange(handler) which I would use in my Sidebar extension to react on entry changes in my Field extension. In which manner does built-in Publish & Status extension works in this case?