I was indeed wrong about this. I’d grown used to uMatrix’s spoofing, where it does get changed, and misrecollected things. I have now refreshed my understanding from the spec: it’s still a parser feature in that that iff scripting is enabled, it parses its children as raw text (like <script> or the old <xmp>). (And then there’s the user-agent style on it, `display: none !important`, so that you can’t get it to appear whatever you do, unlike most normally-hidden tags like head, title and script.)
I apologise for misleading people.