How to set TTL for a document using the Go API client ? What is "exp int"?

I can’t find a reference to TTL or expiry time anywhere in the documentation:

While we’re at it, what “exp int” argument usually used in so many methods, for an example the Add method:, what does it mean ? Also not documented.

I am not the developer. AFAIK, exp is the expiry time in seconds.

Thanks! So apparently no one watches over this questions, should I be using stackoverflow or something else ?