A: Non-seats/members aka "Collaborators" can also comment.
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We really want you to share this with all your clients and collaborators as freely as possible.
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The only requirement will be that they will need to signup (for free) after they attempt to leave a comment. Why? so they can receive email notifications of any followups to their comments.
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When they attempt to comment on a screenshot, they will see this alert if they try to leave a new comment:

They will also see this link if they try to leave a new comment on an existing comment that you shared on the map:
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