This looks really nice but I think it suffers from the same issue a lot of regex tutorials suffer from. It's focusing solely on the regex and not at all on how to actually execute them. This site in particular says it's going to use javascript but at least the first few pages don't show anything except raw regular expressions.

For any tutorial about regular expressions I think the second thing (beyond a very simple example regex) to show should be how to actually execute one in code. Is it that all the tutorials want to be language-agnostic? Maybe just show a javascript example and point out which part is the js function/method call and which part is the actual regex.

It's nice to be told what /[aeiou]/ means but without actually typing it in and executing it (against various inputs, not just one) it wouldn't really sink in for me.