In Xcode 9, Apple has re-engineered the Source Editor entirely in Swift.
For those that don’t know, Source Editor is basically the view in Xcode where you type all of your thousands of lines of code. Think of it as the Microsoft Word part of the Xcode IDE (Integrated Development Environment).
When Apple re-engineered the Source Editor, the performance was dramatically improved, allows you to grow and shrink text and a few other benefits added to it.
But as many developers know, the two main areas of app development in Xcode used the most are the Source Editor and the storyboard.