http://learn.elgg.org/en/3.x/appendix/upgrade-notes/2.x-to-3.0.html#metadata-changes

Thanks

For instance ElggEntity::canComment is used to check if a user cancomment on an entity?
Is there a way to check if an user can access (see or view) an entity ?

Look at these hooks: 1, 2

there is a function `has_access_to_entity()`

https://github.com/Elgg/Elgg/blob/70c2f4535af7b67b690617ebeba74fc59a2b55d2/engine/lib/access.php#L93-L114

http://learn.elgg.org/en/stable/design/events.html#register-to-handle-an-elgg-event is only Elgg core events' list.

You can use elgg_trigger_event() function in your action and register any callback using elgg_register_event_handler() function.

Thanks

from within core there are 2 events bound to each action

first is the 'action:validate' '<actionname>' (eg. blog/save) hook which is triggered before the action is handled

second is the 'response' 'action:<actioname>' (eg. blog/save) hook which is triggered after the action is processed and the response is sent to the user.

See http://learn.elgg.org/en/stable/guides/hooks-list.html#action-hooks

Maybe with one of these 2 you can make it work