Last year, users who used Windows 10 preview builds had access to a set named feature: a tabbed interface that would allow tabs to be added to the title bar of a window. These tabs can be used to combine multiple copies of the same application (for example, a tabbed explorer or prompt), as well as several different windows to group, such as a browser window that contains searches using the Word window. However, on both occasions the feature was only activated for a few weeks so that Microsoft could collect data before it was disabled. Sets are not included in the Windows Update of May 1
The Shell-provided tab experience no longer exists, but adding tabs is at the top of our to-do list.
– Rich Turner (@richturn_ms) April 20, 2019
It now appears that sets are unlikely. Rich Turner, who oversaw Microsoft's redesign of the Windows Command Line Infrastructure and Windows Subsystem for Linux tweeted that the interface is "no more". It is not possible to tabulate everything everywhere. However, adding tabs specific to command-line windows is "high on [Microsoft’s] to do list".
Initially, there was some confusion that the tweet might have required a different system-wide approach to tabs. But Turner today made it clear that the command-line tabs are created specifically for command-line windows, not a common feature for the entire operating system.
Sets were extremely complicated feature. Originally, Microsoft planned to use it only with new programs written using the Universal Windows Platform (UWP). That's because UWP programs generally behave well. Programs created with the old Win32 API can do all sorts of strange things, such as: For example, drawing menus into their title bars (as in Visual Studio), pasting ribbon controls into the title bars (like in Office), or pasting tabs into title bars (like Chrome). In contrast, UWP applications have some control over their title bars, but they are much more controlled and consistent.
However, since most Windows applications use Win32, a pure UWP function would not be useful. In addition, this would have meant that Explorer and the command-line windows were excluded. These are probably the two areas where most tabs are needed. Therefore, Microsoft has expanded the reach of sets and used with Win32 applications. This led to a hugely complex interoperability problem that Microsoft has never cracked properly.
In summary, sets use the tabs developed for the edge browser. With the new Chromium-based Edge, Microsoft is now using the Chromium tab implementation. This eliminates the beautiful features of Edge, such as the flowing design and thumbnails on the tabs. It also means that the company has a much lower interest in maintaining this source code.
Taken together the result? No more sets.