There are quite a few other improvements included in this build; many focus on the reading experience within Windows 10. There are new grammar tools for both EPUB books and Reading View on websites. Additionally, Microsoft Edge has a new look for reading across EPUBs, PDFs and other documents, as well as syncing reading progress and notes across devices. The build also includes support for custom audio in EPUB.
The build adds an option to never save passwords for a domain, which was highly requested feature among Windows Insiders. It also allows for autofilling passwords and using extensions when using InPrivate mode. Additionally, fixes were put in place to make Near Share more reliable. You can see the full list of improvement at the Windows 10 blog.