[XXE] modular docs - proprietary markup?

[pos...@kinetium dot Com]

Is XXE using some propritary markup for containment links in modular
documents? e.g.

    &__copyright__du7diawy;

If so, is there no standard we could follow instead? XLink, XInclude,
XPointer?

e.g. <xi:include href="copyright.html" />

Thanks!