Add a backend to convert boxnotes into DoclingDocument. We can be inspired by the following code
贡献者指南
技术栈
python
领域
backend
议题类型
feature
难度面向新贡献者的预计实现难度，1 表示很小改动，5 表示专家级工作。
3
预计时间有经验贡献者完成调查、实现、测试并准备 pull request 的粗略时间范围。
1-2 days
活动状态议题当前的可参与程度：新鲜、活跃、陈旧、阻塞或等待维护者输入。
fresh
清晰度议题是否清楚说明期望改动、验收标准和下一步。
mostly clear
前置要求
PythonDocling contributor guideBoxNote format
新手友好度1-100 的估计分数，表示该议题对首次贡献者的友好程度。
45
研究方向
The issue asks to add a backend for converting BoxNote files to DoclingDocument. Start by studying the existing backends in the docling codebase to understand the pattern. The referenced code at https://github.com/alexwennerberg/boxnotes2html/blob/main/boxnotes2html/boxnote.py provides a parser for the BoxNote format. The task is to implement a similar converter that outputs DoclingDocument. Since there are no comments or maintainer guidance, it may be necessary to ask for clarification on expected output and integration points.
