code: public String getMostLeftAndMostRightPageAnno() {
  
      if (sspans == null || sspans.isEmpty()) {
        return null;
      }
      TreeMap<Integer, SSpan> rightTokIdxToSSpan = sspans.get(sspans.firstKey());
      SSpan leftSpan = rightTokIdxToSSpan.get(rightTokIdxToSSpan.firstKey());
      SSpan rightSpan = null;
      Integer rightIdx = null;
  
      for (TreeMap<Integer, SSpan> leftIdxValue : sspans.values()) {
        for (Map.Entry<Integer, SSpan> rightIdxEntry : leftIdxValue.entrySet()) {
          if (rightIdx == null || rightIdx <= rightIdxEntry.getKey()) {
            rightIdx = rightIdxEntry.getKey();
            rightSpan = rightIdxEntry.getValue();
          }
        }
      }
  
      if (rightIdx != null) {
        return getPageFromAnnotation(leftSpan)
                + PAGE_NUMBER_SEPERATOR
                + getPageFromAnnotation(rightSpan);
      }
  
      return getPageFromAnnotation(leftSpan);
    }
docs: Creates a String (eg. <b>3-9</b> or <b>3</b>), based on the most left and
  most right page annotation.
  
  <p>The page annotation is detected with
  {@link #getPageFromAnnotation(de.hu_berlin.german.korpling.saltnpepper.salt.saltCommon.sDocumentStructure.SSpan)}</p>
  
  @return A String which represents the start and the end page of a pdf,
  seperated by {@link #PAGE_NUMBER_SEPERATOR}. If there is no end page, or
  exactly one page annotation, only a String with one number is returned.