Tabs … Again (Premium)

Back in the simpler days of the mid-1990s, when Windows was king and native app development was top of mind for developers, Microsoft was actively evolving the platform at a heady pace. With the ultimate aim of moving to an object-oriented system, the software giant first pressed forward with what it called a document-centric interface in which users would focus on the documents that they created rather than the applications they used to do so. But everything was up for grabs, from the presentation of the user experience to basic task navigation to inter-application communications.

Windows 95 was the ultimate expression of this document-centric user interface, and thanks to deep integration with the Microsoft Office 95 applications, users could create new Word documents and Excel spreadsheets right from the Start menu without first opening the relevant application. Indeed, much of the innovation of this era was happening inside of Office instead of Windows. And it was Office that often went to market first with new user interfaces which, if successful, would then be pulled into Windows itself.

Some of these innovations were minor---borderless toolbar buttons, for example---while others, like the ribbon, were revolutionary and even controversial. But in the mid-1990s, Office most obviously established itself as the arbiter of new user interfaces by formally introducing a new concept, called the Multiple Document Interface (MDI), which Microsoft’s developers would race to support for third parties in the Microsoft Foundation Classes (MFC) for Visual C++.

Before this, most Windows applications employed what’s now called a Single Document Interface (SDI) design in which an application could display just a single document---or child window---inside of the main application window frame. So those that needed to open multiple documents at the same time would open multiple instances of the application.

With MDI, applications could optionally host multiple documents---child windows---inside of a single main application window.

Today, this concept is well-understood thanks to web browsers, which are technically MDI applications in which each tab is a child window displaying its own document (a web page). (This is sometimes called a Tabbed Document Interface, or TDI, because the tabs/documents can't float within the main window.) But web browsers also let you open new documents (web pages) in their own windows. This is desirable because different people work in different ways. Some prefer all of their tabs to be in a single window, while others might prefer having two or more browser windows open.

The big issue with MDI is navigation. Because the Alt + Tab feature in Windows was designed to support individual windows, there was no easy way for users to switch between different documents at the OS level. Instead, they could use Alt + Tab to switch to the application window and then some other navigation system---Ctrl + Tab with br...