What does "comment internally" actually mean in JIRA Service Desk?

[Ji]

In JIRA Service Desk projects, comments are segregated by internal vs external visibility. Meaning that I am able to select whether I want to Share with customer or Comment Internally.

Which users are able to see comments that are specifically marked as internal?

I couldn't find proper documentation describing this feature.

[Nic Brough [Adaptavist]]

Share with customer makes the comment visible to everyone who can see the issue/request.

Internal comments do not appear on the requests, so a customer can not see them.

[William Raendchen]

Internal comments are not shown on the portal view of the issue. However, everyone who can see the internal version of the JIRA ticket can see both internal and external comments!

Internal = "Everyone who uses JIRA and has access to this issue in JIRA itself. But not displayed on the portal view"

[Linda Wanitschek]

Thank you William.  Very clean statement.

[Michael Aniskovich]

I still remain confused by this.  "But not displayed on the portal view".

So, I respond to the submitter by tagging them (using the [~nnnnn] tag.

1.) Will they see it if I choose "Comment Internally"?

2.) What parameters constitute "Customer"?  (My assumption is that it's someone outside of my company, but I could be wrong.)

I would LOVE to see "hover-over" notes added to these kinds of things.  Kind of annoyed.

[Linda Wanitschek]

If a user chooses "Raise a Request"  on the customer portal view, there are comments displayed there.

The comments displayed on the Customer Portal View are only the comments where "Customer" is selected.

When Internal is selected the comments are displayed on the Issue view.

Customer is a person who is a reporter or any other person who can see the issue only thru the Customer Portal.

[William Raendchen]

Edit: in addition to what Linda said (which was all correct).

Service Desk has an *additional* representation for Issues, called Portal view.

Internal comments are never displayed in the portal view. However they are displayed in the traditional issue view for everyone who has access to it, i.e. browse permission in your project. 

To restrict customers, who also happen to have access to your JIRA internally, you need to remove those people, as well as the Reporter from the "Browse Project" permission, and replace it with "Service desk customer - portal access".
Then it is ensured that customers can no longer see internal comments. However since they can't see internal tickets anymore, they can also not link them or do anything else with them. [~username] notifications only work if you have access to an internal ticket as well. Servicedesk automatically sends its own notifications, which are seperate from your JIRA notifications.

Sorry if I can't explain it any clearer, in my opinion the way Atlassian set this up is a complete joke and lazy design.