This procedure is defined in the server but not documented via ad_proc or proc_doc and may be intended as a private interface.
The procedure is defined as:
proc xotcl::self {arg} { switch $arg { "" {::uplevel ::nsf::self} next { set handle [::uplevel ::nsf::current nextmethod] method_handle_to_xotcl $handle } default {::uplevel ::nsf::current $arg} } }