When a 4D database is opened in Project mode, the project files are not locked by the application while in Design mode. As a result, the underlying text‑based project files can be accessed simultaneously by external applications without preventing 4D from operating normally. As long as the external application does not place an exclusive lock on the file, modifications can be saved and will be reflected in 4D

For example, if a method file is opened in a text editor while the 4D project is running, edited, and saved, the updated content will appear when the method is opened in the 4D Method Editor. The project system automatically detects changes to the underlying file and reloads the updated version

This behavior enables development workflows that involve multiple tools. External editors can be used to take advantage of features not available in the 4D Design environment—such as advanced search, refactoring tools, or version‑control‑oriented editing, while still maintaining full compatibility with the running 4D project.