code: func (b *Bitmap) Check() error {
  	var a ErrorList
  
  	// Check each container.
  	citer, _ := b.Containers.Iterator(0)
  	for citer.Next() {
  		k, c := citer.Value()
  		if err := c.check(); err != nil {
  			a.AppendWithPrefix(err, fmt.Sprintf("%d/", k))
  		}
  	}
  
  	if len(a) == 0 {
  		return nil
  	}
  	return a
  }
docs: // Check performs a consistency check on the bitmap. Returns nil if consistent.