XEmbed protocol ( X Window System)
XEmbed is a protocol that uses basic X mechanisms such as client messages and reparenting windows to provide embedding of a control from one application into another application. Some of the goals of the XEmbed design are:
Support for out-of process controls, written in any toolkit or even plain Xlib.
Support for in-process-controls when mixing different toolkits in one process.
Smooth integration of the embedding application and embedded client in areas such as input device handling and visual feedback.
Easy implementation. A full implementation supporting all details correctly may require minor toolkit modifications, but it should be possible to get basic functionality going in less than 1000 lines of code.
Reference :
http://standards.freedesktop.org/xembed-spec/xembed-spec-latest.html