Extending PyPDFPatra

This guide explains how to add new features, CSS properties, or layout boxes to the PyPDFPatra engine.

Adding a New CSS Property

Parser Update: If the property is a shorthand, add it to src/pypdfpatra/engine/styling/shorthand.py.
Style Resolution: If the property should follow specific inheritance rules, update INHERITED_PROPERTIES in src/pypdfpatra/engine/styling/resolve.py.
Layout Logic: Implement the property handling in the relevant formatting context:
- src/pypdfpatra/engine/layout/block.py for block boxes.
- src/pypdfpatra/engine/layout/inline.py for inline/line-wrapping.
Rendering: Update src/pypdfpatra/render.py to draw the effects of the new property (e.g., shadows, gradients).

Cython Model: Define the new Box class in src/pypdfpatra/engine/tree.pyx. Ensure it inherits from Box or a relevant specialized subclass.
Box Generation: Update the factory logic in src/pypdfpatra/engine/layout/box_generator.py to instantiate your new box based on display styles or HTML tags.
Layout Context: Create or update a layout function in src/pypdfpatra/engine/layout/ to handle the geometry calculations for the new box.
Renderer: Update draw_boxes in src/pypdfpatra/render.py to handle the painting of the new box type.

Add a sample HTML file in example/ or a new test case in tests/.
Run the coverage script to verify the visual output:
```
python example/test_coverage.py
```