Do not use.
This expectation provides for headers to be examined before potentially large uploads are sent.
At the moment, Apache will not pass control over to the csi18n service until all your data has been uploaded, including your entity-body. The service will only then get to look at your headers, and provide the appropriate response.
If you do use
Expect: 100-continue, csi18n will emit an X-Warning-N header that the expectation has been ignored.
Supporting 100-continue may be implemented in the future.