Nerdy internals of an Apple text editor

This article is the second part of a series on the internals of Paper, a text editor for Apple platforms, and it explains how Paper is built as a TextView-based editor. It says Paper currently uses the older TextKit 1 framework, though the concepts it covers still exist in TextKit 2. The text describes TextView as a layered system: NSTextStorage holds the raw string and its attributes, NSTextContainer defines the shape hosting glyphs, NSLayoutManager computes glyph layout, and TextView draws and manages input and selection. It also explains that Paper uses custom meta attributes from its Markdown parser to mark syntax, then applies styling attributes in a transaction-based update process.