A namespace that contains bits and pieces of Tcl that are either non-kosher or liable to change without warning (experimental, strange, etc.)
Tcl 8.5 has within it:
Tcl 8.6 also has:
AMG: If memory serves, once upon a time Tcl had commands called unsupported0, unsupported1, unsupported2, etc. Once they were finalized, they were renamed. For example, I'm pretty sure fcopy used to be known as unsupported0.
I greatly prefer the namespace approach to segregating the unsupported commands.