magit-section

# magit-section: Collapsible Section-Based UIs

magit-section is Emacs's premier library for creating interactive, hierarchical buffer interfaces with collapsible sections. Originally extracted from Magit, it provides the foundation for building information-dense UIs that users can navigate and explore efficiently.

## Overview

magit-section enables creation of buffers with tree-like, collapsible content organized into sections. Each section can contain nested child sections, custom keybindings, associated data, and responsive highlighting.

**Key Characteristics:**
- Hierarchical collapsible sections with visibility control
- Section-specific keymaps and actions
- Built-in navigation commands
- Visibility caching across buffer refreshes
- Mouse and keyboard interaction
- Integrated with Emacs region selection
- Requires Emacs 28.1+

**Version:** 4.2.0+ (January 2025)
**Repository:** https://github.com/magit/magit
**License:** GPL-3.0+

## Core Concepts

### Section Object

Sections are EIEIO objects with these slots:

- `type` - Symbol identifying section kind (e.g., `file`, `commit`, `hunk`)
- `value` - Associated data (filename, commit SHA, etc.)
- `start` - Buffer position where section begins (includes heading)
- `content` - Buffer position where body content starts
- `end` - Buffer position where section ends
- `hidden` - Visibility state (nil=visible, non-nil=hidden)
- `children` - List of child sections
- `parent` - Parent section reference
- `keymap` - Section-specific key bindings
- `washer` - Function for deferred content generation

### Buffer Structure

Every magit-section buffer requires a single root section that spans the entire buffer. Sections form a tree hierarchy with proper nesting.

### Visibility States

Sections can be:
- **Fully visible** - Heading and all content shown
- **Hidden** - Only heading visible, content collapsed
- **Heading-only** - Nested sections show only headings

## API Reference

### Creating Sections

#### magit-insert-se