Me too. Question is, which way is neatest. Can it be done with one char? In fact, I'm fairly convinced it can't. I can come up with several two-char changes which make it work, but no one-chars.
Ok. given that there's spoilers on here already, and a post explaining why it's broken:
which of these did you think cleaner (my vote is for the first)
(0|$a|$b|$c|$d) < 256
($a+0|$b|$c|$d) < 256
The key here is that | (a bitwise operator) will operate on pairs of chars if both of it's args are a string. In other words, for
"abc" | "def" it does ("a"|"d").("b"|"e").("c"|"f"). However, if either arg has been used in a numeric expression, the evaluation will be done with both sides as a number.