It may be you pressed Enter in error. But it's more likely the issue that's been explained before about using certain symbols- see this thread https://www.theanswerbank.co.uk/Media-and-TV/Question1614571.html
Anything that looks like HTML is going to be reacted to as it could otherwise affect what happens when the page is viewed. Specifically avoid the 'less than' and the 'greater than' symbols.
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