The point of it
The aim is to show overlapping content in text files.
Here the coloured areas show very great similarity between two versions of news text.
How to do it
Choose up to 3 texts. The program looks for overlapping content and colours the views. You can pull each view wider or narrower as you prefer.
The next screen-shot shows two texts with much less similarity, though they share some header information.
See also : duplicate file-names, duplicate contents.