QMarkdownTextEdit is a mature C++ Qt library providing a feature-rich markdown text editor widget, QMarkdownTextEdit, which extends QPlainTextEdit with live markdown syntax highlighting, code block syntax highlighting (for dozens of languages via a large hand-curated keyword dataset), line numbers with bookmark indicators, block (rectangular) selection, clickable links, and an integrated search/replace widget. The library is designed to be embedded into larger Qt applications such as QOwnNotes, Notes, and CuteMarkEd-NG. It supports both widget-based (QWidget) and Qt Quick (QML) integration through a registered QML type. The architecture is a single-library module with optional demo and QML example applications. The core components include the main editor widget, the markdown highlighter (which can be used independently on any QTextDocument), a separate search/replace widget (QPlainTextEditSearchWidget), and a line number area (LineNumberArea). The language-specific syntax highlighting data is generated in a single massive C++ file (qownlanguagedata.cpp) using a consistent pattern of init/load functions grouped by language. The library is built and installed via qmake (.pro/.pri) and CMake, with continuous integration across multiple Qt versions (5.9 to 6.10) on Linux, macOS, and Windows. The codebase is well-organized and demonstrates solid engineering practices: clear separation of concerns (highlighter, search widget, editor), support for internationalization (translation files for German, Spanish, Urdu, Chinese), and compatibility with both widget and QML interfaces. While the library is primarily a UI component, it also includes utility patterns like debounced search and regex support. The main risk is the maintenance burden of the enormous hand-curated syntax data file, which contains some minor errors and duplicates, and the lack of automated tests for the highlighting logic. Overall, this is a practical, production-grade text editor component with broad applicability in Qt projects requiring markdown or code editing capabilities.