How to mention someone in an idea comment section

To mention someone in the comments of an idea, select the challenge you'd like to do so in from the challenge homepage.

Select the idea from the idea list you'd like to comment on

Scroll to the bottom of the submission page and input the @ symbol followed by the user's name you'd like to mention. Select their name from the drop down menu. NOTE: if the user hasn't created an account or accepted their invite, their name will not appear. Click post when your comment is complete. 

The mention will now display in the comments thread of the idea.