At the top level, there are general categories like expression evaluation. At lower levels the events become more specialized, such as function, operator, procedure, and assignment activity. Events are color coded and scroll in the region at the center of the window. Clicking on a line in the code region in which a structure is created marks that structure for subsequent tracing. The histogram region shows a list of structures being traced.
Colors code the number of evaluations on a line.
The source code can be set to scroll or move to the currently executing line. Font size can be changed to accommodate programs of different sizes. The user can set break points in the program and then examine the contents of structures when a break point is encountered. There are value browsers that can be used, for example, to inspect the contents of structures interactively. Clicking on a value in a structure brings up a browser for that value.