code: func (p Bits) ColumnIDs() []uint64 {
  	if p.HasColumnKeys() {
  		return nil
  	}
  	other := make([]uint64, len(p))
  	for i := range p {
  		other[i] = p[i].ColumnID
  	}
  	return other
  }
docs: // ColumnIDs returns a slice of all the column IDs.