Introduction

Currently window creation (and to some extend also cross-window communication) on the web platform works using window.open() are follows:

• window.open() synchronously returns a reference to the newly created window.
• window.opener returns a reference to the window that opened the window (i.e. the application main document).

However, window.open() does not address the following requirements (for related use cases, refer to the Application Lifecycle and Events specification):

• An application must be able to create a window that is initially hidden.
• An application must be able to create a new window that does not block the main thread of the application, i.e. the API for creating a new window must be asynchronous.
• The runtime must be able to stack modal windows, relevant in both mobile and especially desktop context. If windows are stacked modally, multiple windows must not be shown in the task switcher.
• An application should be able to ask another application to create a window and be able to integrate the newly created window in its modal window stack hierarchy.

This specification defines an API for creating windows that addresses the requirements.