The source for decode_entities_old, which I thought was just a pure-Perl version of decode_entities, looks roughly like this (I've stripped out some context dependence):
sub decode_entities_old
{
my $array = [ @_ ];
my $c;
for (@$array) {
s/(&\#(\d+);?)/$2 < 256 ? chr($2) : $1/eg;
s/(&\#[xX]([0-9a-fA-F]+);?)/$c = hex($2); $c < 256 ? chr($c) : $1/
+eg;
s/(&(\w+);?)/$entity2char{$2} || $1/eg;
}
return @$array;
}
With this code, and the under-populated hash my %entity2char = ( amp => '&', quot => '"' ), we have
say decode_entities_old '&amp;quot;'; => "
say decode_entities_old '&#x26;quot;'; => &quot;
We would get (essentially) the opposite behaviour if we switched the second and third substitutions; that's what I mean by “This is very particular to the ordering”.
Of course, your example shows that decode_entities (which I guess is implemented in XS—I couldn't find it in the source) doesn't exhibit this buggy behaviour, so I guess that there's a reason that the sub I quoted has _old postpended. :-)
UPDATE: I just noticed that I'd mangled my intended bug-inducer, &quot;, above. I wonder if decode_entities (not decode_entities_old) handles it correctly?
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