XLIB Programming Manual, Rel. 5, Third Edition

12.4 Selections

Selections are the primary mechanism X11 defines for clients that want to exchange information with other clients. A selection transfers arbitrary information between two clients. You can think of a selection as a piece of text or graphics that is highlighted in one application and can be pasted into another, though the information transferred can be almost anything. Clients are strongly encouraged to use this mechanism so that there is a uniform procedure in use by all applications.

The user may want to transfer information from an application and, at other times, to the application. Many applications need to be able to assume either role. In particular, clients should not display text in a permanent window without allowing the user to select it and convert it into a string, and any application that requires the user to type extensively should allow the user to paste in text from other applications.

Selections communicate between an owner client and a requestor client. The owner has the data representing the value of a selection, and the requestor wants it. The selection mechanism provides a way to notify other clients when useful data is placed in a property and to allow the owner of the data to convert it to a type asked for by the requestor.

Note that in the X11 environment, all data transferred between clients must go via the server (unless they are running on the same host, but that is a special case). An X11 client can neither assume that another client can open ...