express links

[modond]

In
Express ('E' in MEAN)
here " We use Express to set up our web server. Skim the Express documentation and then take a look at..."

This is the express-link you meant (I think);
http://expressjs.com/

Now, the express and documentation links point to expressjs.org (a domain for sale).
Earlier in the documentation (explaining the MEAN stack at introduction) you used the correct link.