assign to object by offset

Is there any reason that zend_assign_to_object always converts the property to a string when it's a variable? Looking at simpexml, there is no way to distinguish between writing to an element or to an attribute when using variables. $sxe[0] = "a"; works fine, but $i=0; $sxe[$i] = "a"; doesnt as $i is sent to the write_dimension function as a string while 0 is passed as is. Due to this $sxe[0] will write the value to the element, while $sxe[$i] will write it to the attribute. Reading however works fine as no conversion is done on the zval. Thanks, Rob