If you want to comment on an event, just go to the "Events" module and find the event you want to comment on in the "Event calendar" and Click on it. A small window will pop up and at the top are different menu options for the event. By choosing "Comments", you can see all the existing comments and post your own comment.

Use the text field to write your comment and click on the red plus sign on the right to make it public.

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