XES recognizes and treats all extensions as equal, independent from their source. This allows users of the format to extend it, in order to fit any purpose or domain setting. However, there are recurring requirements for information stored in event logs, which demand a fixed and universally understood semantics. For this purpose, a number of extensions have been standardized. When creating logs for a specific domain, or also when designing log-analyzing techniques, one should consider using these standardized extensions, since they allow for a wider level of understanding of the contents of event logs.
In the sidebar, links to the currently standardized extensions can be found.