@0xabad1dea I used an XML-esque passphrase (something along the lines of <FooBarBaz/>) on PlentyOfFish circa 2013 because they demanded special characters even for absurdly long passphrases.
It worked fine.
Until my now-wife and I got serious enough I decided to delete my account. I had to type my password on the "delete account" page and for whatever reason on that page only (but not the login form or the creation page), it tripped the WAF and blocked the deletion.
I ended up experimenting a bit and discovered that I could still *change* my password and as soon as I had a password without angle brackets in it, I was able to delete the account.
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