ok, looking at programming language pragmatics it seems like you want fairly serious (university level) theory. so i don't understand why people are talking about regexps - that should be covered in a subsection (regular grammars) of one chapter of that book. anyway, for databases i would suggest date's "sql and relational theory" - it shows how sql is related to a more elegant, cleaner, underlying theoretical approa…
The author of the post made mention of the knowledge applying to web development and then said the following towards the end of the post:
the difference would be in a higher focus on practical application
Regular Expressions is kind of the tl;dr on the topic. They are practical to web development but require a deeper understanding of a particular area of computing.
I took his post to say, I want to go deep, I want it to be applicable to real world web development, and I want it to be targeted topics. I think regular expressions fit that bill. Sure there are others, and maybe some overlap but I personally mentioned regular expressions because it has a high degree of misunderstanding, but also a high degree of usefulness in web development.