New experimental command added in ::tcl::unsupported on 2009-12-07.
Docs forthcoming, for now just the tclcore thread at [L1 ]
May only be called from within a coroutine.
AMG: Why is this command named with an internal capital letter? All other built-in Tcl commands (as opposed to utility procs) are named with multiple words (or abbreviations thereof) jammed together with no capitals or underscores. Examples abound: [bgerror], [fblocked], [filename], [foreach], [gets], [lappend], [regexp], [uplevel], and [vwait].
MS no special reason