> I don't mean to make this into a code golf thread

Too late. Golfing notes:

• Your `win` variable is unnecessary: window is approximately the global object (look into globalThis for the subtleties of how window isn’t quite the global object), so you can drop your “win.” every time, e.g. win.c.removeChild(b) can be just c.removeChild(b).

• parent.appendChild(child) → parent.append(child) and parent.removeChild(child) → child.remove(), using newer, shorter DOM methods.

• Skip quotes on attribute values, and trailing slashes are 100% superfluous in HTML (they’re explicitly ignored, as an XHTML compatibility mechanism; I reckon they’re actually a slightly bad thing rather than harmless).