void add(Page page)

Adds a page to the end of this book.

If this page is in any book, it is first removed from that book.

Source 

void add(Page page) {
  if (page.book != null) {
    // Re-adding the page to the end; ignore updates.
    if (_active == page) _active = null;
    page.book.remove(page);
  }
  page.book = this;
  _pages.add(page);
  if (_active == null) _active = page;
  page._display = _active == page ? _display : _displayNone;
  page.onEvent(PageEvent.added, this);
  log("added $page");
}