Graylog Message Categories - Need help in finding unique value mappings

We are exploring the graylog message categories, so that we can categorise the syslogs in our requirement.

We saw that in the graylog schema : Graylog Message Categories — Graylog (GIM) Schema 3.5 documentation

gim_event_type_code is mapped to some unique values, like : “100000”,“|authentication|”,“|logon|”,“logon”

Can somebody please tell how is this value 100000 decided?
For example : for authentication it is 100000
For iam it is 110000,
For name resolution it is 140000.

Are these any random unique values decided or any logic is there behind those values.
Please tell.

Thanks in advance.