Wow... I am honoured and embarrassed that my very old article about building a web search engine in PHP is on that list.
I should replace it with how to do it in a language I actually like working with one of these days... and generally improve it because its missing all sorts of niceties such as skip lists on the posting lists, binary formats for saving things.
I also noticed all the code is missing as a result of the conversation from Wordpress to Hugo... fixing that now.
EDIT - fixed, but might need a refresh from anyone who visited it.