\Q and \E don't work inside interpolations. They only work in regexp literals

Fascinating theory, but easily proven wrong:

print "\Qabc*def\E\n"; # prints abc\*def
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The truth is that \Q means "add backslashes to special chars until \E" in the exact same places that \n becomes a newline and $x expands to its value: every double-quoted string. A regex (that doesn't have special single-quote quoting) is just one example of that.