code: func (ix *IndexWriter) addName(name string) uint32 {
  	if strings.Contains(name, "\x00") {
  		log.Fatalf("%q: file has NUL byte in name", name)
  	}
  
  	ix.nameIndex.writeUint32(ix.nameData.offset())
  	ix.nameData.writeString(name)
  	ix.nameData.writeByte(0)
  	id := ix.numName
  	ix.numName++
  	return uint32(id)
  }
docs: // addName adds the file with the given name to the index.
  // It returns the assigned file ID number.