docs: function shortenIDs(startNumber) {
    if(_.isUndefined(startNumber)) {
      startNumber = 1;
    }
    var $identifiedElements = $('[id]');
    var referencedIDs = findReferencedElements();
  
    // scour:
    // > Make idList (list of idnames) sorted by reference count
    // > descending, so the highest reference count is first.
    // > First check that there's actually a defining element for the current ID name.
    // > (Cyn: I've seen documents with #id references but no element with that ID!)
  
    var idList = _(_(referencedIDs).keys()).filter(function(id) {
      return ($identifiedElements.find('#' + id).length > 0);
    });
    idList = _(idList).sortBy(function(id) {
      return referencedIDs[id].length;
    }).reverse();
  
    _(idList).each(function(id) {
      var shortendID = intToID(startNumber++);
  
      // scour:
      // > First make sure that *this* element isn't already using
      // > the ID name we want to give it.
      if(id == shortendID) {
        return;
      }
      // scour:
      // > Then, skip ahead if the new ID is already in identifiedElement
      while($identifiedElements.find('#' + shortendID).length > 0) {
        shortendID = intToID(startNumber++);
      }
      // scour:
      // > Then go rename it.
      renameID(id, shortendID, $identifiedElements, referencedIDs);
      
    });
  
  }