docs: function make_then(th) {
                  if (th == null) return ";";
                  if (th[0] == "do") {
                          // https://github.com/mishoo/UglifyJS/issues/#issue/57
                          // IE croaks with "syntax error" on code like this:
                          //     if (foo) do ... while(cond); else ...
                          // we need block brackets around do/while
                          return make_block([ th ]);
                  }
                  var b = th;
                  while (true) {
                          var type = b[0];
                          if (type == "if") {
                                  if (!b[3])
                                          // no else, we must add the block
                                          return make([ "block", [ th ]]);
                                  b = b[3];
                          }
                          else if (type == "while" || type == "do") b = b[2];
                          else if (type == "for" || type == "for-in") b = b[4];
                          else break;
                  }
                  return make(th);
          }