The problem is that ’ decodes to the Unicode character U+0092, UTF-8 C2 92, known as PRIVATE USE TWO:
$ php test.php | xxd
0000000: 5374 616e c292 73 Stan..s
I.e., this doesn't decode to a usual apostrophe.
html_entity_decode($string) works because it doesn't actually decode the entity, since the default target charset is latin-1, which cannot represent this character. If you specify UTF-8 as the target charset, the entity is actually decoded.
The target of that entity is the Windows-1252 charset:
echo iconv('cp1252', 'UTF-8', html_entity_decode('Stan’s', ENT_QUOTES, 'cp1252'));
Stan’s
Quoting Wikipedia:
Numeric references always refer to Unicode code points, regardless of the page's encoding. Using numeric references that refer to permanently undefined characters and control characters is forbidden, with the exception of the linefeed, tab, and carriage return characters. That is, characters in the hexadecimal ranges 00–08, 0B–0C, 0E–1F, 7F, and 80–9F cannot be used in an HTML document, not even by reference, so ™, for example, is not allowed. However, for backward compatibility with early HTML authors and browsers that ignored this restriction, raw characters and numeric character references in the 80–9F range are interpreted by some browsers as representing the characters mapped to bytes 80–9F in the Windows-1252 encoding.
So you're dealing with legacy HTML entities here, which PHP apparently doesn't handle the same way "some" browsers do. You may want to check if the decoded entities are in the range specified above, that you transcode/redecode them in Windows-1252, then convert them to UTF-8. Or require your users to pass valid HTML.
This function should handle both legacy and regular HTML entities:
function legacy_html_entity_decode($str, $quotes = ENT_QUOTES, $charset = 'UTF-8') {
return preg_replace_callback('/&#(d+);/', function ($m) use ($quotes, $charset) {
if (0x80 <= $m[1] && $m[1] <= 0x9F) {
return iconv('cp1252', $charset, html_entity_decode($m[0], $quotes, 'cp1252'));
}
return html_entity_decode($m[0], $quotes, $charset);
}, $str);
}
