A Lab combines text and executable J code in a single file. The Lab system lets you step through the file, displaying the text and executing the code. The user is in a normal J session, and can try out other J expressions while running through the lab.
The J IDEs provide menu access to labs. For example in the Qt IDE, select menu Help|Studio|Labs...
A Lab is structured into one or more chapters, each containing one or more sections. The user can go through chapters in any order, but the sections within each chapter are run sequentially.