code: func (ix *Index) listAt(off uint32) (trigram, count, offset uint32) {
  	d := ix.slice(ix.postIndex+off, postEntrySize)
  	trigram = uint32(d[0])<<16 | uint32(d[1])<<8 | uint32(d[2])
  	count = binary.BigEndian.Uint32(d[3:])
  	offset = binary.BigEndian.Uint32(d[3+4:])
  	return
  }
docs: // listAt returns the index list entry at the given offset.