When constructing a complex regular expression, it may be helpful to construct by hand the intended output for comparison with the result of executing the regular expression. If provided, comparison data is displayed in an additional window located below the result window. This window is not initially present but is added if the user indicates the intention to enter comparison data. Like test input data, comparson data may be loaded from a file, entered in the associated window or constructed by editing data loaded from a file.
If comparison data is supplied, the program will automatically compare the actual output with the intended output and report on any differences. Comparisons may also be triggered by means of a menu button, located on the File menu. This allows the user to correct errors in the comparison data, or test a hypothesis about what is wrong, by editing the data in the window and rerunning the comparison.
If the result of execution of the regular expression differs from the comparison data, a message to this effect appears in the message window and a display of the differences pops up. In the example below, the display indicates that the comparison data lack the word "queues" which is present in the result of execution of the regular expression.
If the result of execution of the regular expression is the same as the comparison data, a message to this effect appears in the message window.