I have something confused on the "Errors" and "IsValid" property of BulkResponse

Hi,I have something confused on the "Errors" and "IsValid" property of BulkResponse.

When there is something wrong with Elasticsearch when i create index,assume the service of Elasticsearch stopped, the value of IsValid is false and the value of Error is false.

When there is no wong with Elasticsearch and no wrong in bulk insert action when i create index,the value of IsValid is true and the value of Error is false.

When the Elasticsearch is normal,but some data failed when the Elasticsearch do bulk insert action when create index, the value of IsValid is false and the value of Errors is true.

So I am confused on the meaning of the value of "IsValid" and "Errors" stands for,I also get knowledge on that the The BulkResponse.Errors property pertains to actual bulk insert errors (inserting duplicate records, etc...).

Could anybody give me some Inspirations? I use the Nest client,the version of it is 2.2.
Thank you !