New experimental command added in ::tcl::unsupported on 2009-12-07.
Suspends the current coroutine and makes the current coroutine's caller invoke command (with the optional args). Command is resolved prior the suspension in the context of the current coroutine, and can refer to another coroutine (though this is not required). May only be called from within a coroutine; it is an error to call it from elsewhere.
Exceptions:
Docs forthcoming, for now just the tclcore thread at [L1 ]
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
CRC From the thread, it appears that the author of this code just likes, or is used to, camel case. In the ensuing discussion it was referred to as "yieldto". Not being a fan of camel case myself, I hope that if it gets incorporated, it is "yieldto", or "yield -target" as DKF suggests.