Description:
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PHP Array manual:
"Floats are also cast to integers, which means that the fractional part will be 
truncated. E.g. the key 8.7 will actually be stored under 8."

But this rule is ignored by SimpleXML object's array.

Test script:
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$xml = simplexml_load_string("<xml><number>0</number><number>1</number></xml>");

$i = (int) 1;
$d = (float) 1;

$xml->number[$d] = 999;

echo $xml->number[$d] .", ". $xml->number[$i];

Expected result:
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999, 999

Actual result:
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999, 1