Test handling of empty lines.

Test mixed line height.

Test shaping across intra-word breaks.

Test with only directionally neutral characters.

Add shaped runs output for bidirectional text.

Add tests for mixed text direction.

Test interaction between boxes and mixed script.

Test soft breaking on box spacing.

Test line breaking in boxes.

Test layout with mixed font sizes.

Test Rich pagination.

Test Rich line wrapping.

Test Rich layout.