While randomly browsing through the page source of Stack Overflow, I came across a closing </partial> tag in the page source of Stack Overflow. I went ahead and checked the page source of a few Stack Exchange sites and it seems that this is the case for all pages of all Stack Exchange sites.
This looks like a leftover part of Razor markup, specifically the partial tag helper. The partial tag helper is a self-closing tag:
<partial name="_Xyz" /> and it may have been used like an opening and closing tag:
<partial name=_Xyz"></partial> And what we see on the source page is the closing tag.
It may also be that a partial view intended to be included is not being included in the page markup.
</partial>Replace:. Ship It! 🚀