Extensions to X

X was designed to be extensible. Anyone can invent an extension to the protocol for their own use. Most people who develop X extensions eventually submit them to the X Consortium to be added to the distribution. Two of the more popular extensions are Display PostScript and PEX (PHIGS Extensions to X). Other extensions to support multiple input devices, video, and compressed images have been suggested or added.

Problems:

• each extension must be analyzed for new security problems;
• if a client requires the use of an extension that the target server does not support, the application will fail;
• each extension increases the size of the server and client libraries, which can make clients less likely to be responsive in a timely manner;
• supporting an extension typically creates more work for the server, which can decrease availability;
• less popular extensions are likely to be less robust;
• the run-time requirements of an extension may limit its use to more expensive platforms, or may decrease its robustness on low-end platforms.