TextKit 2 Reference

Use this skill when you already know the editor is on TextKit 2 and need exact APIs, object roles, or migration details.

When to Use

• You are working with NSTextLayoutManager, NSTextContentManager, or fragments.
• You need viewport-layout or migration details.
• You are writing TextKit 2 code directly rather than choosing between stacks.

Quick Decision

• Need to choose between TextKit 1 and 2 -> /skill apple-text-layout-manager-selection
• Already committed to TextKit 2 and need exact APIs -> stay here
• Need fragment/rendering behavior specifically -> /skill apple-text-viewport-rendering

Core Guidance

Complete reference for TextKit 2 (iOS 15+ / macOS 12+). Replaces glyph-based TextKit 1 with element-based layout optimized for correctness, safety, and performance.

Keep this file for the object model, editing rules, and layout-manager behavior. For fragment internals, object-based range mechanics, and the TextKit 1 to 2 mapping table, use fragments-and-migration.md.

Architecture

NSTextContentManager        NSTextLayoutManager         NSTextContainer
(content model)        →    (layout controller)    →    (geometry)
       │                           │                         │
NSTextContentStorage        NSTextLayoutFragment         UITextView
(wraps NSTextStorage)       NSTextLineFragment           NSTextView
       │                           │
NSTextElement               NSTextViewportLayoutController
NSTextParagraph             (viewport management)

Design Principles

1. Abstraction — No glyph APIs. International text (Arabic, Devanagari, CJK) handled correctly without character-glyph mapping assumptions. Trade-off: glyph-level work requires TextKit 1 or Core Text.
2. Safety — Immutable value semantics for elements and fragments. Thread-safe reads.
3. Performance — Always non-contiguous. Only viewport text is laid out. O(viewport) not O(document).

NSTextContentManager (Abstract)

Base class for content management. Manages document content as a tree of NSTextElement objects.

Key Properties

var textLayoutManagers: [NSTextLayoutManager] { get }
var primaryTextLayoutManager: NSTextLayoutManager? { get set }
var automaticallySynchronizesTextLayoutManagers: Bool  // default: true
var automaticallySynchronizesToBackingStore: Bool       // default: true

Editing Transaction

All text storage modifications must be wrapped:

textContentManager.performEditingTransaction {
    // Modify the backing store (NSTextStorage) here
    textStorage.replaceCharacters(in: range, with: newText)
}
// Layout invalidation happens automatically after the transaction

Without the transaction wrapper: Element regeneration and layout invalidation may not occur correctly.

Element Enumeration

textContentManager.enumerateTextElements(from: location, options: []) { element in
    if let paragraph = element as? NSTextParagraph {
        print(paragraph.attributedString)
    }
    return true  // continue enumeration
}

Delegate

// Filter elements from layout (e.g., hide comments in a code editor)
func textContentManager(_ manager: NSTextContentManager,
                        shouldEnumerate textElement: NSTextElement,
                        options: NSTextContentManager.EnumerationOptions) -> Bool

NSTextContentStorage (Concrete)

Default NSTextContentManager subclass. Wraps NSTextStorage and automatically divides content into NSTextParagraph elements.

Relationship to NSTextStorage

let textContentStorage = NSTextContentStorage()
textContentStorage.textStorage = myTextStorage  // Set backing store

// Access text storage from content storage
let storage = textContentStorage.textStorage

NSTextContentStorage observes NSTextStorage edits and regenerates paragraph elements automatically.

NSTextContentStorage vs NSTextStorage

Aspect	NSTextStorage	NSTextContentStorage
Role	Backing store (attributed string)	Content manager wrapping backing store
Addressing	NSRange (integer-based)	NSTextRange / NSTextLocation (object-based)
Output	Raw attributed string	NSTextElement tree (paragraphs)
Editing	Direct mutations	performEditingTransaction wrapper
Notifications	processEditing()	Element change tracking
When to subclass	Custom backing store format	Custom content model (not attributed string based)

Decision: Use NSTextContentStorage (default) unless you need a fundamentally different backing store (e.g., database-backed, DOM-based, piece table). In that case, subclass NSTextContentManager directly.

Delegate

// Create custom paragraph elements with modified display attributes
// WITHOUT changing the underlying text storage
func textContentStorage(_ storage: NSTextContentStorage,
                        textParagraphWith range: NSRange) -> NSTextParagraph? {
    // Return nil for default behavior
    // Return custom NSTextParagraph to override display
    let originalText = storage.textStorage!.attributedSubstring(from: range)
    let modified = NSMutableAttributedString(attributedString: originalText)
    modified.addAttribute(.foregroundColor, value: UIColor.gray, range: NSRange(location: 0, length: modified.length))
    return NSTextParagraph(attributedString: modified)
}

Range Conversion

// NSRange → NSTextRange
let textRange = textContentStorage.textRange(for: nsRange)

// NSTextRange → NSRange
let nsRange = textContentStorage.offset(from: textContentStorage.documentRange.location,
                                         to: textRange.location)

NSTextElement

Abstract base class for document building blocks. Immutable (value semantics).

Properties

var elementRange: NSTextRange? { get set }  // Range within document
var textContentManager: NSTextContentManager? { get }
var childElements: [NSTextElement] { get }    // For nested structures
var parentElement: NSTextElement? { get }
var isRepresentedElement: Bool { get }

NSTextParagraph

Default element type. One per paragraph of text.

let paragraph: NSTextParagraph
paragraph.attributedString     // The paragraph's attributed content
paragraph.paragraphContentRange // Range excluding paragraph separator
paragraph.paragraphSeparators   // The paragraph separator characters

NSTextLayoutManager

Replaces NSLayoutManager. No glyph APIs. Operates on elements and fragments.

Key Properties

var textContentManager: NSTextContentManager? { get }
var textContainer: NSTextContainer? { get set }
var textViewportLayoutController: NSTextViewportLayoutController { get }
var textSelectionNavigation: NSTextSelectionNavigation { get }
var textSelections: [NSTextSelection] { get set }
var usageBoundsForTextContainer: CGRect { get }
var documentRange: NSTextRange { get }

Layout Fragment Enumeration

// Enumerate visible layout fragments
textLayoutManager.enumerateTextLayoutFragments(
    from: textLayoutManager.documentRange.location,
    options: [.ensuresLayout, .ensuresExtraLineFragment]
) { fragment in
    print("Frame: \(fragment.layoutFragmentFrame)")
    for lineFragment in fragment.textLineFragments {
        print("  Line: \(lineFragment.typographicBounds)")
    }
    return true  // continue
}

Options:

• .ensuresLayout — Forces layout computation (expensive for large ranges)
• .ensuresExtraLineFragment — Includes empty trailing line fragment
• .estimatesSize — Use estimated sizes (faster, less accurate)
• .reverse — Enumerate backwards

Rendering Attributes

Replace TextKit 1's temporary attributes. Overlay visual styling without modifying text storage:

// Set rendering attributes (replaces any existing)
textLayoutManager.setRenderingAttributes(
    [.foregroundColor: UIColor.red],
    forTextRange: range
)

// Add rendering attributes (merges)
textLayoutManager.addRenderingAttribute(.backgroundColor,
                                        value: UIColor.yellow,
                                        forTextRange: range)

// Remove rendering attributes
textLayoutManager.removeRenderingAttribute(.backgroundColor, forTextRange: range)

// Enumerate rendering attributes
textLayoutManager.enumerateRenderingAttributes(
    from: location, reverse: false
) { manager, attributes, range in
    return true
}

Key difference from text storage attributes: Rendering attributes don't persist, don't modify the model, and don't trigger element regeneration.

Invalidating Layout

// Invalidate specific range
textLayoutManager.invalidateLayout(for: range)

// TextKit 2 re-lays out affected fragments on next viewport update

Delegate

// Custom layout fragments (e.g., chat bubble backgrounds)
func textLayoutManager(_ manager: NSTextLayoutManager,
                       textLayoutFragmentFor location: NSTextLocation,
                       in textElement: NSTextElement) -> NSTextLayoutFragment {
    return BubbleLayoutFragment(textElement: textElement, range: textElement.elementRange)
}

Common Pitfalls

1. Using ensuresLayout for the full document — O(document_size). Only ensure layout for visible ranges.
2. NSTextLineFragment.characterRange is local — It's relative to the line's attributed string, NOT the document. Convert through the parent element.
3. renderingSurfaceBounds differs from layoutFragmentFrame — Drawing can extend beyond the layout frame (diacritics, large descenders). Override renderingSurfaceBounds in custom fragments.
4. Forgetting performEditingTransaction — Direct NSTextStorage edits may not trigger proper element regeneration.
5. Assuming layout exists outside viewport — TextKit 2 may only have estimated layout for off-screen content. Use .estimatesSize option when precision isn't needed.

Related Skills

• For fragment APIs, viewport controller hooks, range conversion, and migration tables, see fragments-and-migration.md.
• Use /skill apple-text-layout-manager-selection for migration and stack choice.
• Use /skill apple-text-viewport-rendering for fragment and rendering-pipeline behavior.
• Use /skill apple-text-storage for backing-store and editing-transaction background.