To find User Manual pages on new and updated features in Unity 2017.3, click on the link above or search for “NewIn20173”.
This lists User Manual pages containing Unity 2017.3’s:
To find out more about the new features, changes, and improvements to this Unity version, see the 2017.3 Release Notes.
If you are upgrading existing projects from an earlier version to 2017.3, read the Upgrade Guide to 2017.3 for information about how your project may be affected.