Notepad4 is a Windows-based source code editor built on the Scintilla editing component. It provides syntax highlighting for over 50 programming languages, dark mode support, a plugin system (including the matepath file browser), and standard editing features such as find/replace, code folding, and auto-completion. The application is designed for developers seeking a lightweight yet feature-rich editor with extensive language support. The architecture is modular, separating the core editor (Notepad4) from plugins like matepath. The core editor uses Scintilla for text rendering and editing, with a custom wrapper (SciCall.h) to provide type-safe access to the Scintilla API. Language-specific lexers are maintained in the src/EditLexers directory, with many generated from keyword lists to ensure accuracy. Configuration is managed via INI files, and localization is supported through resource DLLs for multiple languages. Key external dependencies include Scintilla (for the editing core), Boost.Regex (for regular expression search), and the Windows API (for GUI, shell integration, and system services). The project demonstrates attention to modern Windows features such as Hi-DPI support, dark mode, and multi-monitor awareness. While the codebase is Windows-centric, it maintains clean separation between concerns through well-defined interfaces and encapsulation.