Most popular data formats are regularly revised. The semantics of each target must be well defined to both the source and the destination programs. Remember that the X Window System is an open environment. Your users will expect your products to interoperate properly with products from other vendors. Since you will probably not be able to control or test all combinations of products, you should strive to use well defined, standard targets whenever possible.
Proprietary targets are sometimes useful, but supporting standard ones as well is always good idea.
Recently, I've been working with Mike Chow and Doug Rand of Silicon Graphics' User Interface Technology group to develop a standard list of interchange targets. The list of targets is presented in the next section. These cover the major data types used by commercial multimedia and graphics programs. Hopefully, this will occur in the next release of X. Most of these targets are actually the names of files containing the data. Passing large amounts of data can significantly degrade the performance of your X server.