So I don't want to round-trip the entire form to server just to validate a single field, or download the thousands of possible airport IATA codes to the client each time.

所以，我不希望只是为了验证一个单个字段要在服务器间往返通信整个表单，或者每次都需要将数千个机场的 IATA 编码下载到客户端。

youdao

The codes reveal what kind of airport checks a passenger will face and can be read by smartphones, he says.

BBC: Boarding pass barcodes 'can be read by smartphones'