Windows 10 build 17639 (rs prerelease)

Windows 10 build 17639 is the sixth Insider Preview build of Windows 10 October 2018 Update. This build was released to Windows Insiders that were opted into Skip Ahead on 4 April 2018.

Sets

 * You can now drag and drop tabs within the Set and combine other tabbed app windows into Sets.
 * You can now switch between tabs by using Alt+Tab . You can also customize it to show only the primary window.
 * Updated the settings for Sets in the Multitasking page of the System section in the Settings app. A setting was added to make it either show both windows and tabs or make it just show individual windows. It was also made searchable as well.
 * You don't have to hold down to open a new File Explorer windows in a tab. A new keyboard shortcut was added to open a new tab while File Explorer is in focus, which is CTRL+T . The keyboard shortcuts CTRL+N and CTRL+W can be used to open and close tabs respectively.
 * Added an option to easily open new tabs and windows on the File menu on File Explorer, as well as adding a new "Open in new tab" option on the right-click menu while a folder is selected.
 * Added new context menu options for tabs in Sets. These include “close other tabs”, “move to new window”, and “close tabs to the right”.
 * You can pick and choose which of the previous tabs to restore.
 * You can now restore Previous Tabs from any type of activity.
 * When a document is opened that had tabs previously open, there will be a prompt offering to restore those tabs, and the previous tabs icon will be in the filled state. For sessions that didn't involve documents, the prompt will not appear, but the previous tabs icon is marked as filled regardless.
 * An animation was added to signify if there are no previous tabs to be restored.

General

 * You can now check the battery level of a Bluetooth device.
 * The Calculator app was updated to make it correctly calculate square roots for perfect squares (integers that are squares of other integers). For example, the square root of 2 would display as 1.99999999999999999989317180305609, which would be rounded and displayed as 2, but if that number was subtracted, the incorrect digits would be displayed. With this build's calculator, the square root calculation now recognizes perfect squares and correctly returns exactly 2 for the square root of 4.

General

 * If you click on links to the Microsoft Store in the Settings app, links in the tips section and the link to Windows Defender, the Settings app will crash.
 * You may get to see the desktop before you get to the lock screen upon resuming from stand-by.
 * The Movies & TV app can crash if the user denies access to their video library and then navigates to the Personal tab.

Sets

 * The File Explorer ribbon does not stay pinned if restarted. The app exclusion list in the Sets settings may take some time to populate the first time it's opened.
 * Sometimes it takes two attempts to open up an inactive tab from the taskbar.
 * Sometimes a second row of tabs may be seen when the new tab page is opened.
 * When an app or website is launched from the new tab page, there's a chance that the focus will change to a different tab.
 * Sometimes the "filled" state of the Sets restore icon will remain filled even though all the tabs have been restored.
 * Narrator can read extra text when Alt+Tab is invoked.
 * Sometimes the new tab will be blank. Closing and opening the tab again should resolve this bug.