was looking into how we can make fewer things in #15538 need to be aware of the templating mode (which will make everything more robust) and ran into this <pre> logic. Took me a while to wrap my head round it but it turns out we way overcomplicated things in #14922 — the essence of this logic is that if the first node inside a <pre> is a single newline, we need to strip it because otherwise hydration breaks:

document.body.innerHTML = `<pre>
<div>...</div>
</pre>`;

document.body.querySelector('pre').firstChild; // DIV, not the newline

Instead of doing a convoluted song and dance we can just express that directly. For #15538, we do want to strip any remaining leading newline, but that should happen in template_to_functions, not here