When modifying code in examples with line highlights ({2-4}), always update the highlight line numbers to match the new code. Incorrect line numbers cause rendering crashes.
File Name Conventions
Capitalize file names for component files: Gallery.js not gallery.js
After initially explaining files are in src/, refer to files by name only: Gallery.js not src/Gallery.js
**Version conventions:**
- Use `"latest"` for stable features
- Use exact versions only when compatibility requires it
- Include minimal dependencies (just what the example needs)
### Hidden File Patterns
**Always hide these file types:**
| File Type | Reason |
|-----------|--------|
| `package.json` | Configuration not the teaching point |
| `sandbox.config.json` | Sandbox setup is boilerplate |
| `public/index.html` | HTML structure not the focus |
| `src/data.js` | When it contains sample/mock data |
| `src/api.js` | When showing API usage, not implementation |
| `src/styles.css` | When styling is not the lesson |
| `src/router.js` | Supporting infrastructure |
| `src/actions.js` | Server action implementation details |
**Rationale:**
- Reduces cognitive load
- Keeps focus on the primary concept
- Creates cleaner, more focused examples
**Example:**
```mdx
```js src/data.js hidden
export const items = [
{ id: 1, name: 'Item 1' },
{ id: 2, name: 'Item 2' },
];
### Active File Patterns
**Mark as active when:**
- File contains the primary teaching concept
- Learner should focus on this code first
- Component demonstrates the hook/pattern being taught
**Effect of the `active` marker:**
- Sets initial editor tab focus when Sandpack loads
- Signals "this is what you should study"
- Works with hidden files to create focused examples
**Most common active file:** `src/index.js` or `src/App.js`
**Example:**
```mdx
```js src/App.js active
// This file will be focused when example loads
export default function App() {
// ...
}
### File Structure Guidelines
| Scenario | Structure | Reason |
|----------|-----------|--------|
| Basic hook usage | Single file | Simple, focused |
| Teaching imports | 2-3 files | Shows modularity |
| Context patterns | 4-5 files | Realistic structure |
| Complex state | 3+ files | Separation of concerns |
**Single File Examples (70% of cases):**
- Use for simple concepts
- 50-200 lines typical
- Best for: Counter, text inputs, basic hooks
**Multi-File Examples (30% of cases):**
- Use when teaching modularity/imports
- Use for context patterns (4-5 files)
- Use when component is reused
**File Naming:**
- Main component: `App.js` (capitalized)
- Component files: `Gallery.js`, `Button.js` (capitalized)
- Data files: `data.js` (lowercase)
- Utility files: `utils.js` (lowercase)
- Context files: `TasksContext.js` (named after what they provide)
### Code Size Limits
- Single file: **<200 lines**
- Multi-file total: **150-300 lines**
- Main component: **100-150 lines**
- Supporting files: **20-40 lines each**
### CSS Guidelines
**Always:**
- Include minimal CSS for demo interactivity
- Use semantic class names (`.panel`, `.button-primary`, `.panel-dark`)
- Support light/dark themes when showing UI concepts
- Keep CSS visible (never hidden)
**Size Guidelines:**
- Minimal (5-10 lines): Basic button styling, spacing
- Medium (15-30 lines): Panel styling, form layouts
- Complex (40+ lines): Only for layout-focused examples