Undo support around extendscript command

This probably should be obvious, but how can "undo" be supported for a custom command(in Framemaker 10?  I found app.beginUndoGroup() for another product but frame gives an unknown method call for this.

The following will delete with Ctrl-Q, but "undo" remains greyed out.  Thanks in advance.

function demoDelete() {

    var doc = app.ActiveDoc;

    if (!doc) {

        alert("No active document");

        return;

    }

    var range = doc.TextSelection;

    if (range.beg.offset == range.end.offset) {

        alert("Need to select some text");

        return;

    }

    doc.DeleteText(range);

}

function Command(cmd) {

    app.beginUndoGroup("demoCsr Command");

    switch (cmd) {

    case 1111: {

        demoDelete();

    }

    app.endUndoGroup();

}

var cmd = DefineCommand(1111, "demoCsrXrefInsert", "demoCsrXrefInsert", "^q");