I think the only real way to ensure that a spoiler is spoiler safe is a modification to Perlmonks.org. What if a <spoiler> tag were added to Perl Monks, which would result in a button being displayed. Clicking the button would do a javascript document.write to place the spoiler below the button. Of course, this has it's problems because:
a. this solution involves hacking Perlmonks -- which takes up precious developer time.
b. people aren't always receptive to improvements. I am sure there are people who will think a spoiler button is a bad idea.
c. not everyone has javascript enabled
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