Questions about the mqtt subscription topics

I was subscribing to the topics according to what is written on that page. I tried to subscribe to the ack and to the tx topics but I wasn’t receiving any messages.

However, if I subscribe to “gateway/+/tx” or “gateway/+/ack” I get the appropriate messages. Is this correct, or am I supposed to also get those same messages on the “application” topic?

Are the acks in the application topic acknowledgements of downlinks sent to nodes (node is sending ack) or the other way around? On the wiki page one could grammatically read it as either.

Are the “tx” messages on the application topic only sent when the application sends a message? i.e. publishing?