chain of responsibility - how/when to use?

With a view to improve working of some code, I come across this place ( link) where, how $PATH environment variable is an example of chain of responsibility design pattern, is explained.

While at the outset, I can see that any number of environment variables used in a tool are only useful when they some how are linked to $PATH. (I must be wrong here, as this is not absolute). Can somebody throw more light ( to go deeper ) into it.

As the link that it suggests is not working. ( COR_link )