code: public void assertInvariant() {
          if (start > pages.getSize()) {
              throw new IllegalStateException();
          }
          if (start > pageSize) {
              throw new IllegalStateException();
          }
          if (start > getEndOfs()) {
              throw new IllegalStateException();
          }
          if (end > endFilled) {
              throw new IllegalStateException();
          }
          if (endPage != pages.get(endPageIdx)) {
              throw new IllegalStateException();
          }
      }
docs: --