Description:
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http://de3.php.net/manual/en/function.html-entity-decode.php says:

        Available flags constants
Constant Name   Description
  ENT_COMPAT    Will convert double-quotes and leave single-quotes alone.
  ENT_QUOTES    Will convert both double and single quotes.
  ENT_NOQUOTES  Will leave both double and single quotes unconverted.
  ENT_HTML401   Handle code as HTML 4.01. 
  ENT_XML1      Handle code as XML 1. 
  ENT_XHTML     Handle code as XHTML. 
  ENT_HTML5     Handle code as HTML 5.

However, I don’t see ' being decoded with ENT_QUOTES.

Test script:
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<?php
$x = "&apos;";
$y = html_entity_decode($x, ENT_QUOTES, "UTF-8");
echo "< $y >\n";


Expected result:
----------------
< ' >


Actual result:
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< &apos; >