Exercise 2: Why the Opt-Out Symbol Is Always Visually Distinct — Possible Solution
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THE TWO CHOSEN MECHANISMS
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Blade:  {{ $note }}   (escaped, default)   vs.   {!! $note !!}   (raw)
Pug:    #{note}       (escaped, default)   vs.   !{note}         (raw)

WHY BOTH CHOSE A NEW, UNUSUAL-LOOKING SYMBOL
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In both cases, the "safe" opt-out isn't a hidden flag, a config option,
or a keyword argument tucked away somewhere else in the code -- it's a
different, visually loud character sitting right at the exact spot
where the value gets inserted:

  - Blade doubles up its own curly braces into exclamation marks:
    {!! !!} instead of {{ }}. Exclamation marks read, at a glance, as
    an alarm -- the same instinct that makes "!!" a common way to mark
    something urgent in plain writing.
  - Pug swaps its pound sign for a bang: !{ } instead of #{ }. A bang
    (!) carries the identical "warning" connotation in nearly every
    programming context a developer has likely already seen it in.

If either system instead used, say, a boolean second argument
(escape(note, false)) or a config toggle set once per template, the
"this value is unescaped" fact would be genuinely easy to miss while
reading the template later -- a reviewer scanning the file would have
to already know to go looking for it. Putting a visually different
symbol directly at the point of use means the unsafe spot is
impossible to skim past. Anyone reading {!! $note !!} or !{note} sees,
immediately and without extra context, that this one specific value is
being trusted rather than protected.

THE SAME PRINCIPLE, DIFFERENT SPELLING
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This is exactly the same real design decision Chapter 4's own
SafeString class made, and the same one every other system in this
chapter's own big table makes, whatever the exact symbol: React's
dangerouslySetInnerHTML spells the danger out as an actual English
word in the prop's own name; EJS distinguishes <%= %> from <%- %> with
a single different character; Django/Jinja2 use a named |safe filter
instead of a symbol, but the filter's own name is doing the identical
job -- making the decision to skip escaping something a reader has to
consciously notice, not something that can happen by accident.

WHY THIS WORKS AS AN ANSWER
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It picks two genuinely different-looking real symbols from the
chapter's own table, explains the concrete readability problem a
hidden flag or config option would create instead, and connects both
back to the single underlying design principle -- make the unsafe path
visually loud -- that the chapter's own finding-box already identified
as shared across every system checked.