How ProseMirror's Mark Preservation Logic Breaks Markdown Editor Design

This article uncovers a subtle interaction between ProseMirror's text mark preservation system and markdown editor assumptions. When joining text blocks, marks are correctly preserved by design, but markdown editors store visual properties like boldness in both node types and inline marks, causing unintended style bleeding. The author demonstrates a practical plugin-based solution that cleanly intercepts the join operation to strip inherited marks.