[[Explain theory of [Tcl]'s private interfaces.]]















As "[Migration to 8.4: Tk Private Commands]" explains,
there was a particular issue in the transition of [Tk] from 8.3 to 8.4.
Details appear in the source distribution in
    library/unsupported.tcl
which installs as
    local/lib/tk$VERSION/unsupported.tcl