update docs and gitignore

.gitignore

@@ -45,9 +45,12 @@ test_output/
 examples/output/
 
 # Generated data
-
+bookmarks/
 positions/
 
+# Profiling scripts
+profile_*.py
+
 # Debug scripts output
 debug_*.png
 .fish*

FONT_SWITCHING_FEATURE.md

@@ -0,0 +1,139 @@
+# Dynamic Font Family Switching
+
+The pyWebLayout ereader now supports dynamic font family switching, allowing readers to change fonts on-the-fly without losing their reading position.
+
+## Visual Demo
+
+![Font Family Switching](docs/images/font_family_switching_vertical.png)
+
+*The same content rendered in Sans-Serif, Serif, and Monospace fonts*
+
+## Features
+
+- **Three Bundled Font Families**: Sans-Serif (DejaVu Sans), Serif (DejaVu Serif), and Monospace (DejaVu Sans Mono)
+- **Dynamic Switching**: Change fonts instantly during reading
+- **Position Preservation**: Your reading position is maintained across font changes
+- **Attribute Preservation**: Bold, italic, size, and color are preserved when switching families
+- **Automatic Cache Management**: Intelligent cache invalidation ensures optimal performance
+
+## Usage
+
+```python
+from pyWebLayout.style.fonts import BundledFont
+from pyWebLayout.layout.ereader_manager import create_ereader_manager
+
+# Create an ereader instance
+manager = create_ereader_manager(blocks, page_size=(600, 800))
+
+# Switch to serif font
+manager.set_font_family(BundledFont.SERIF)
+page = manager.get_current_page()
+
+# Switch to monospace font
+manager.set_font_family(BundledFont.MONOSPACE)
+page = manager.get_current_page()
+
+# Restore original fonts
+manager.set_font_family(None)
+page = manager.get_current_page()
+
+# Query current font family
+current_family = manager.get_font_family()  # Returns BundledFont or None
+```
+
+## API Reference
+
+### EreaderLayoutManager Methods
+
+#### `set_font_family(family: Optional[BundledFont]) -> Page`
+
+Change the font family and re-render the current page.
+
+**Parameters:**
+- `family`: Font family to use (`BundledFont.SANS`, `BundledFont.SERIF`, `BundledFont.MONOSPACE`, or `None` for original fonts)
+
+**Returns:**
+- Re-rendered page with the new font family
+
+**Example:**
+```python
+# Switch to serif
+page = manager.set_font_family(BundledFont.SERIF)
+
+# Restore original fonts
+page = manager.set_font_family(None)
+```
+
+#### `get_font_family() -> Optional[BundledFont]`
+
+Get the current font family override.
+
+**Returns:**
+- Current font family (`BundledFont.SANS`, `BundledFont.SERIF`, `BundledFont.MONOSPACE`) or `None` if using original fonts
+
+**Example:**
+```python
+family = manager.get_font_family()
+if family:
+    print(f"Currently using: {family.value}")
+else:
+    print("Using original fonts")
+```
+
+## Font Families
+
+### Sans-Serif (BundledFont.SANS)
+- **Font**: DejaVu Sans
+- **Best for**: Screen reading, modern interfaces
+- **Characteristics**: Clean, legible, no decorative strokes
+
+### Serif (BundledFont.SERIF)
+- **Font**: DejaVu Serif
+- **Best for**: Long-form reading, formal documents
+- **Characteristics**: Traditional, classic appearance with decorative strokes
+
+### Monospace (BundledFont.MONOSPACE)
+- **Font**: DejaVu Sans Mono
+- **Best for**: Code, technical documentation
+- **Characteristics**: Fixed-width characters, uniform spacing
+
+## Examples
+
+### Complete Demo
+See [examples/11_font_family_switching_demo.py](examples/11_font_family_switching_demo.py) for a full demonstration including:
+- Creating ereader content
+- Switching between font families
+- Navigating with different fonts
+- Position tracking across font changes
+
+### Generate README Images
+Run [examples/generate_readme_font_demo.py](examples/generate_readme_font_demo.py) to create comparison images:
+```bash
+python examples/generate_readme_font_demo.py
+```
+
+## Implementation Details
+
+The font family switching is implemented using a **hybrid approach** that combines:
+
+1. **FontFamilyOverride class**: Manages font preferences at render time
+2. **Font transformation pipeline**: Intercepts and transforms Font objects during rendering
+3. **Intelligent caching**: Automatic cache invalidation when font family changes
+4. **Backward compatibility**: Works with existing Font-based content without migration
+
+This approach provides:
+- ✅ No breaking changes to existing code
+- ✅ Instant font switching without document recreation
+- ✅ Preservation of font attributes (weight, style, size, color)
+- ✅ Optimal performance with intelligent buffering
+
+## Technical Notes
+
+- Font family changes invalidate the page buffer cache
+- Reading position is preserved using the abstract document structure
+- Background rendering adapts to the new font family automatically
+- All three bundled fonts are included in the package (license: Bitstream Vera / Public Domain)
+
+## License
+
+The bundled DejaVu fonts are free and open source under the [Bitstream Vera License](pyWebLayout/assets/fonts/DEJAVU_README.md).