TextKit goes back to the NeXT era, before Mac OS X was a thing. After the relatively new Cocoa frameworks for Mac app programming were introduced and introduced the “Cocoa Text System” title, iOS and UIKit stuck with “TextKit”, and in 2021 TextKit 2 returned.
This revolves around everything related to accepting textual user input on the Mac:
NSTextViewfor the UI component,
NSTextStoragefor the processing of text and style changes,
NSLayoutManagerfor the computation of line and glyph sizes, and for applying styles,
NSTypesetterfor putting glyphs on the screen.
NSTextFields are just reusing a shared
NSTextView, called the window’s field editor. It’s everywhere.
- TextKit API docs: describes all core components and, since TextKit 2, comes with sample projects and WWDC links.
- TextKit 2 Introduction (WWDC 2021)