CoreText

Core Text is a low-level application programming interface (API) used in macOS and iOS to display and handle text. It is part of the Core Graphics framework and provides a comprehensive set of functionalities for text rendering, layout, and manipulation. Core Text allows developers to have fine-grained control over how text appears on the screen, including advanced typographic features.

The API is built upon other Apple frameworks such as Core Foundation and Core Graphics. It exposes powerful capabilities that are utilized by higher-level frameworks like UIKit's text system and AppKit's text rendering. Core Text is responsible for tasks such as glyph generation, text shaping, line breaking, and the application of various text attributes like fonts, colors, and styles.

Developers can leverage Core Text to implement custom text layouts, handle complex scripts and bidirectional text, and integrate advanced typographic features like ligatures and alternates. It provides access to font metrics and glyph information, enabling sophisticated text styling and manipulation. While powerful, Core Text is a low-level API, meaning it requires more direct coding compared to higher-level text handling solutions.