From this version onward the default storage model for XMLType is not CLOB but Binary XML. This has the advantage that due to its Binary XML nature Oracle can optimize XML handling because the format of the XML document or instance is known. Also Oracle can, if possible, transport XML binary format, so smaller in size, data in and out the database if used with the binary XML API’s. Another advantage handling content driven queries, is the possibility of query rewrites or optimizing memory objects, so called XOB objects which are more efficient or smaller in size.
See the Oracle XMLDB Developers Guide 11.2.0.x for more info.
…and this concludes my first post via an Android phone…