In addition to adding default bookmarks, it could make sense to display a short grayed out text in the form of “Do XXX to add your own bookmarks here” on the bookmark bar whenever it is empty.
This would avoid confusion even if a user deletes the default bookmarks, but then does not add any of their own. Also, if for some reason all the bookmarks get deleted from there, it would look less like a display bug.
I’m not sure if we really need that. “Manage bookmarks” from the bookmarks menu should be sufficient, at least in my view. It already opens ~/config/settings/WebPositive/Bookmarks in Tracker. You can easily move/remove/edit bookmarks in the bookmark bar from there.
+1 for that. In addition to that the user could also select into which folder (if any) the new bookmark should be put. By folder I mean subfolders in the main bookmarks folder of course
First and foremost you should look at what does an inexperienced user do? What would you do if you had no idea.
I think you should set up a favourites/bookmarks management that allows you to move/link one of the existing bookmarks to the bookmarks bar.
Then the name should be shortened automatically. However, allow the name to be changed later, through administration.
It reintroduces the confusion of “Web+ shows a weird empty menubar” which is why the bookmark bar auto-hiding was added in the first place. If we allow to make it visible, the “…” menu should be replaced by a disabled “No bookmarks in bookmark bar yet” item.
Also the “…” menu is supposed to show only when there are too many bookmarks and the window is too small to show them all. But this code never quite worked as expected.
We can’t fit a paragraph of userguide text here 
The bookmark bar should just say that it is a bookmark bar (which isn’t obvious when it’s empty), and accepts drag and dropped Web+ pages and/or tabs, URLs, and bookmark files.
There shouldn’t be too much confusion since the bookmark bar is disabled by default anyway. If I enable the bookmark bar in the menu and an empty bar appears it should be obvious this is the bookmark bar I just enabled. Maybe I’m just expecting too much from the user 
To me it made more sense to have it always enabled (no setting). And just have it disappear if you don’t have any bookmarks there. That would be simpler. But users deleting or renaming the folder will be confused on how to have the bar come back.
Once again I lean towards the idea that using Tracker to manage all things isn’t such a great idea…
Of course I don’t mean a whole paragraph, something very concise like “Drop tabs here to add bookmarks”. But I see your point.
If drag and drop being is of the primary ways to populate the bookmarks bar, having it hidden when empty may not be a great experience since the user would then have to use a different method to add their first bookmark, or the bar suddenly disappearing on them after they delete the last (default) bookmark.
I´m inclined to agree on that, but from what I picked up from discussions in the community over the years I somehow got the feeling it was an integral part of the “Haiku way”.
The main reason the “Haiku way” is not a written document somewhere and just general agreement between people, is that we can change our minds.
I never was happy with using Tracker for everything, I find it quite unconvenient. Having bookmarks as separate files is nice and a lot better than an sqlite database as it is done in other browsers. I can share bookmarks easily with other people. I can package some with my apps if I want to. I can transport them between browsers. This is great. But, I don’t think Tracker should be the main way to do things. In this example “oh you just need to create a folder named ‘Bookmark bar’ and the bookmark bar will magically show up in the browser” is not a good user experience. It is not discoverable, you can’t guess that’s how it works.
Same is true to Haiku’s E-Mail app!?
The files are in the folders and easy to handle and to read and to store/restore for a long time!?