code: function () {
              var currState = inputStateObj || new TextareaState(panels);
  
              if (!currState) {
                  return false;
              }
              if (mode == "moving") {
                  if (!lastState) {
                      lastState = currState;
                  }
                  return;
              }
              if (lastState) {
                  if (undoStack[stackPtr - 1].text != lastState.text) {
                      undoStack[stackPtr++] = lastState;
                  }
                  lastState = null;
              }
              undoStack[stackPtr++] = currState;
              undoStack[stackPtr + 1] = null;
              if (callback) {
                  callback();
              }
          }
docs: Push the input area state to the stack.