gistfile1.txt

  /**
    Invokes the callback for each index. Otherwise works just like regular 
    forEach().
    
    @param {Function} callback
    @param {Object} target
    @returns {SC.IndexSet} receiver
  */
  forEachIndex: function(callback, target) {
    var content = this._content,
        cur     = 0,
        source  = this.source,
        next    = content[cur];

    if (target === undefined) target = null ;
    while (next !== 0) {
      while(cur < next) { 
        callback.call(target, cur++, this, source) ; 
      }
      cur  = Math.abs(next);
      next = content[cur];
    }
    return this ;
  },