Is there a function which lets you add functionality to an existing app on ios?

I am curious if it is possible to make an app that adds a functionality to an existing app on ipad, say safari. If yes, which function would add a button to safari?

My question is based on 2 app advertisements I saw, one added a开发者_StackOverflow中文版 button to safari, the other created an app itself. I didnt buy them yet, so I dont know if they really do what thet say. Thanks

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As far as I'm aware, I think the closest you get to adding functionality to an existing app would be creating a new app that allowed interaction with certain document types.

For example, you might create an app that can open and read PDF documents. On installing this app, you would then find that interacting with a PDF document on any app (such as in an email attachment, or opening a PDF in Safari) would show a new option to open the PDF in your app. This kind of interaction is achieved via the UIDocumentInteractionController class.

Beyond that, I believe you would have to create your own app from scratch based on an existing one in order to extend functionality (so, create the 'MyBrowser' app to behave like Safari, except with additional controls and features).

I'd love to be proven wrong, however.