<question>
    <type_elt>
        <opt_out_flag />
    </type_elt>
</question>

if (xml.*.opt_out_flag) {
    do_something();
}

xml..opt_out_flag

if( "opt_out_flag" in xml.children()[0] ) {
    doSomething();
}

var optOutNodes:XMLList = xml.descendants("opt_out_flag");

if(optOutNodes.length())
{
   //do code here
}

var optOut:Boolean = xml..opt_out_flag != undefined