Last night thanks to @orman I had the epiphany of why:

XML parsers don't use or even need regex to parse XML in the first place.

XML parsers go through the text one char at a time, and if they encounter a <, >, </, or />, those chars form flags that signal to the parser if it's entering or leaving a tag, and whether it's a closing or self-closing tag respectively, all of which changes the parsing rules and builds a node tree on the fly.

This will be useful for the UTC.