return vSubstring.New(this, start, start + s.length());
return vSubstring.New(var, start, start + s.length());
public vVariable Assign(vDescriptor x) {    vString s = x.mkString();		// coerce assigned value    var.Assign(vString.New(this.strval(), start, end, s));    return vSubstring.New(this, start, start + s.length());}