Description:
------------
documentation ( http://php.net/manual/en/filter.filters.sanitize.php ) states:

filter_var, option FILTER_SANITIZE_FULL_SPECIAL_CHARS: Equivalent to calling htmlspecialchars() with ENT_QUOTES set.
but in reality, the two differ.

the FILTER_SANITIZE_FULL_SPECIAL_CHARS is missing the FILTER_FLAG_ENCODE_AMP flag (which is not even documented for that filter) to actually be equivalent to htmlspecialchars() as documented.

Test script:
---------------
$STRING = "1 2";
echo htmlspecialchars($STRING, ENT_QUOTES)."\n".
     filter_var($STRING, FILTER_SANITIZE_FULL_SPECIAL_CHARS)."\n";

1 2
1 2

Expected result:
----------------
following the documentation, I expect 

filter_var("1 2", FILTER_SANITIZE_FULL_SPECIAL_CHARS)

to return

1 2

Actual result:
--------------
1 2