"Semantic" means making all distinctions you care about and not making any distinctions you do not care about. This means a custom notation for nearly every case. XML is such a tool. And XSLT is a key component to make all these notations compatible with each other.
That is not what "semantic web" means. Semantic web was a series of standards (rdf and friends) made by w3c from the early 2000s that didnt really catch on.
