Programmatically Add Tabs to NSWindows without NSDocument
The Cocoa/AppKit documentation is very sparse when it comes to tabbing. You can make use of the native window tabbing introduced in macOS Sierra with a few simple method calls, though. Conceptually, this is what you will need to do: However, there are some caveats when implementing these methods naively. The plus button may stop working (no new tabs are added when you click it) and all default shortcuts are broken, their main menu items greyed out.