Actions Play vs PlayPlause vs Select?

Could someone please share exactly what the different actions does in Kodi?
(I’m looking into customizing keyboard.xml)
What are the differences between Select, Enter, Play and PlayPause? The in-depth differences…
The “OK” button on my CEC (TV) remote will work both as Select and when music is playing it’ll do PlayPause.
Why is my IR remote with a keyboard keymap different? Select will start playing a file but no pause. PlayPause will not Select?