docs: void setAnchor(int page, Map.Entry anchor) {
          SimpleImmutableEntry anchorEntry = new SimpleImmutableEntry(page, anchor);
          int anchorCount = anchorList.size();
          if (page < anchorCount) {
              anchorList.set(page, anchorEntry);
          } else if (page == anchorCount) {
              anchorList.add(anchorEntry);
          } else {
              throw new IllegalArgumentException("Anchor index is not correct, expected: " + page + " found: " + anchorCount);
          }
      }