A feature of 4D 21 is the ability to fully expose an uncompiled component to the host database in designer mode. In designer mode, any uncompiled component included with the host database can have its source viewed and modified as if the component was being interacted with directly in design mode. The code can also be debugged directly using breakpoints or by adding a TRACE.

These changes allow for the use and development of components to be more convienent without the need to continously restart the separate structures for testing and fixing.