[LegionMammal978]

> which is also what the page you linked is using

To be clear, it's using both of them for different purposes, you'll find both <use> elements and <!ENTITY> declarations in files like https://kingbird.myphotos.cc/packing/square-11.svg. You can't <use> a numeric quantity in an attribute, the closest alternative for those would be CSS variables.

As for the existence of <use>, I agree with jarek-foksa, the idea is that the original element and all its clones from <use> are linked in the DOM at runtime, as opposed to DTD entities which are baked in textually. Also, most people hate XML, I'd imagine they'd hate internal DTDs doubly so, especially with how little information can be found about them outside the XML standard.

(Browser devs also love to beat the drum of minimizing attack surface, so it's a bit surprising that DTDs and XML stylesheets still work at all. I'd expect them to tear out that functionality in a heartbeat if it were ever used in a modern exploit.)