The Problem
In my now long time I am working as a software-developer and software-architect, I often discovered problems with standard controls for forms. Most of them belong to the category "non-scaling" or lazy-loading.Tabs
If you want to use tabs to group data you might run into difficulties when the number of tabs is unknown at developing time. What happens? If you need to put many tabs inside your form, the space they need becomes larger. If they don't fit in one row, another row needs to be shown. You might run out of space. Another issue arises when a user is allowed to close a tab. If not all tabs have the same width, a user won't be able to close multiple tabs at one time, because the location of the close-button always changes.Treeview
Although there is no control in HTML5-Standard, this control is often used in Desktop-Applications and sometimes also created as a replica on webpages. On the side of each node you usually have a plus-sign that can be used to expand nodes that are located below.A plus-sign should only be visible, if an element has sub-elements. So imagine what happens, if you need to fill the data to such a control. Lazy loading would mean, that you list the top elements and then do a query for each of those elements, if it has subitems. That sounds really crazy. Maybe that's the reason, why control like that is not part of HTML-standards.