Just a note, right now I have a tab item that has visible set to a formula. The problem is that the tab isn't visible in design mode once this is set. It works fine when running the application, it displays when the formula equals true and hides when it's false. But if I'm trying to edit the tab, I have to set visible to true in order to see the tab and then set it back to the formula afterwards. This isn't ideal. It's not a massive issue, but it is a bit of a problem from a maintenance perspective.
There are other users that don't want hidden tabs to appear in design time. I am afraid we can't support both at the same time.
Really? That's so strange. I get your dilemma. But I really fail to see how not seeing a tab in design mode would be useful. Did those other users say why they didn't want to see it in design mode?
Here is the thread (it is about DataGrid columns but the sentiments are the same).
I read the thread, and I have to disagree that the sentiments are the same for this reason. In the data grid, even if you set a column's visible to false, you can still edit, change and redesign the column through the grid's columns editor.
The tab situation is much closer to how you handle controls and forms, where you can set visible to false, but you still are able to edit it in design mode. The form and control doesn't go invisible in the design mode and for good reason. You can't edit anything if you can't see it. This is the situation with the tabs as well. There's no way to edit a tab and even more importantly the controls on a tab, if visible is set to false. And seeing that it's likely that there's a formula that decides if a tab is visible/not visible, you're now forcing the developer to store that formula, set the tab to visible, make the changes and then remember to reset that formula for visible. This seems pretty onerous to me and hopefully you'll see the distinction and reconsider how you handle it.
I guess this is one of the cases when we can't make everybody happy. People that have lots of tabs will complain that all of a sudden they are all visible in design time (happened in a communication with a customer over email that I shall not disclose). The workaround to make the tab visible is not that cumbersome after all. The opposite - hiding a tab in design time when you have 10 or more - will not be possible.