Exercise 1: Three "Self-Closing" Divs in a Row — Possible Solution
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THE TEST
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    tokenize("<div/><div/><div/>Hi</div></div></div>")

RESULT
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    [opentag('div', {}), opentag('div', {}), opentag('div', {}),
     text('Hi'),
     closetag('div'), closetag('div'), closetag('div')]

    kinds: ['opentag', 'opentag', 'opentag', 'text',
            'closetag', 'closetag', 'closetag']

WHAT A REAL BROWSER WOULD RENDER
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Three divs, genuinely nested three levels deep, with "Hi" as the
content of the INNERMOST one -- not three empty, self-closed boxes
sitting next to each other. Visually: a single block of text reading
"Hi", wrapped by three levels of (by default, invisible) div
containers, one inside the next. Nothing about the "/" characters
changed anything about the final structure at all -- the markup
behaves exactly as if it had been written "<div><div><div>Hi</div>
</div></div>" from the start, with the div tags containing no
trailing slashes anywhere.

WHY THIS WORKS AS AN ANSWER
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Every one of the three "/" characters gets stripped and discarded by
tokenize's own self_closing_slash handling, but NONE of the three
div tag names appear in VOID_ELEMENTS -- so every single one falls
through to the plain `opentag` branch instead of `voidtag`. Because
opentag never synthesizes a matching closetag the way a real
self-closing element would, all three divs stay genuinely open,
waiting for real closing tags -- and the three real </div> tags at
the end of the source are exactly what closes them, one level at a
time, from the innermost outward. This is the same finding the
chapter itself demonstrated with a single div, just scaled up to
make the "it silently nests instead of self-closing" behavior
impossible to miss.