Hi all, I'm new with AEM and I'm working with 6.4.3 version, I'm trying to intercept the action when activating a page through classic UI, can someone give a clue on how to achieve this approach??
Thanks in advance.
PD: My idea is to avoid publishing a page which has a bad reference to an Asset, or validate some conditions in the content before let author activate the page for example, and show up some dialog with some message.
You can create/edit the existing replication workflows and add some approval step if it does not already have such step. This doc might be useful to you: Adobe Experience Manager Help | Replicating Adobe Experience Manager Content using the Replication A...
You could try disabling the activate button and modify the "Request for activation" workflow as required. So each page which needs activation has to go through this workflow if the requirement has to be achieved.
If you would like to achieve this through the activate button, there's room to customize replication agent like the below example 
Thanks you for the suggestions, they were really helpful to find some clues to achieve this, at the end i found the asset references dialog and overlay it to disable activate dialog button when the needed conditions match, the js was ReferenceSearchDialog.js which handle the activation process when the OOTB implementation found unpublished assets or outdated, so I also found de ServletSearchReferences to populate the data needed for UI validations.