Your username here MUST MATCH your XenForo username (connected to your XF license).

    Once you have registered here, then you need to start a conversation at xenforo.com w/Bob and provide the following:
    1. Your XenForo License Validation Token
    2. The Domain Name associated with the License
    NOTE: Your account will be validated once ALL requirements are verified/met. Thank you for your patience.

Conditional "is author"

in what context? The item record contains the field "user_id" which is the author of the item. There are several case where there are checks to see whether the viewing user is the owner of the item (or items).

I need you to give me a specific example of what you are trying to do in order to help.
I only wanted the author to leave comment, so I will add conditional statement to check whether the user is the author of the item, and show the comment box only if the user is the author.