According to Microsoft, the main changes in PP4 over PP3 are:
- Cross-Origin Resource Sharing (CORS) for safe use of XMLHttpRequest across domains.
- File API Writer support for blobBuilder allowing manipulation of large binary objects in script in the browser.
- CSS user-select property to control how end-users select elements in a Web page or application.
- Support for HTML5 video text captioning, including time-code, placement, and captioning file formats.
The ongoing additions of HTML5 features had turned IE10 into a browser that can now compete with its rivals in terms of HTML5 support. It is still behind Firefox and Chrome, but IE10 has passed Opera and Safari. When Can I Use shows that IE10 supports 83 percent of HTML5 recommended, proposed, and working draft features. IE9 is at 52 percent, while Firefox is currently at 86 percent, and Chrome at 89 percent. Safari is at 77 percent and Opera at 70 percent.
It is safe to assume that, until the final release, Microsoft will continue on this path and aim to turn IE10 into a compelling HTML5 browser specifically on Windows 8.