Understand base64 encode id for Github v4 API

Recently when querying to github, the ID field for an entity decribes it self as “Represents a unique identifier that is Base64 obfuscated. It is often used to refetch an object or as key for a cache. The ID type appears in a JSON response as a String; however, it is not intended to be human-readable. When expected as an input type, any string (such as “VXNlci0xMA==”) or integer (such as 4_) input value will be accepted as an ID_.”

When I decode an Id as -

>>> b64decode('MDQ6VXNlcjMzODI4OTQy').decode('utf-8')

“User” signifies entity, and the number signifies databaseID?

What does “04” prefixed to “:” mean/ signify?

The underlying structure of the IDs is undocumented and subject to change at any time.

I hope that helps.