PHP XPath Query XML?

我试图制作一个PHP文件，可以在XML文档中搜索特定的鱼。这是我写的：

$FISH_NAME = $_POST["fish_name"];
$LOCATION = $_POST["location"];
$STATUS = $_POST["status"];
$EDIBLE = $_POST["edible"];
$SCS_NAME = $_POST["scs_name"];
$COLOR = $_POST["color"];
$FEATURE = $_POST["feature"];

$varsPassed = array(
    $FISH_NAME => "NAME", 
    $LOCATION => "@LOCATION", 
    $STATUS => "STATUS", 
    $EDIBLE => "EDIBLE", 
    $SCS_NAME => "SCS-NAME", 
    $COLOR => "COLORS/COLOR", 
    $FEATURE => "FEATURES/FEATURE"
);
$conditional = "";
function addToCond($varPassed, $tagName) {
    if (!empty($varPassed)) {
        if(!empty($conditional)) {
            $conditional .= " and {$tagName} = '{$varPassed}'";
        }
        else {
            $conditional = "{$tagName} = '{$varPassed}'";
        }
    }
}
foreach($varsPassed as $current_feature => $current_tag_name) {
    addToCond($current_feature, $current_tag_Name);
    echo "{$current_feature}: {$current_tag_name}'n";
}
$query = "/FISHDICT/FISH[@LOCATION = 'REEF']";
echo $query;
$dom = new DOMDocument();
$dom->load('server/fish.xml');
$xpath = new DOMXpath($dom);
$value = $xpath->evaluate($query);
foreach($value as $item) {
    echo "found:  {$item->nodeValue}'n'n";
}

但它不起作用。我在网页上得到了回应：

Angelfish：名称：特征/特征/FISHDICT/FISH[@LOCATION='REEF']

有人知道为什么它不循环通过每个后变量吗？

XML:

    <FISH location="REEF">
    <NAME>Angelfish</NAME>
    <COLORS>
        <COLOR> Blue </COLOR>
        <COLOR> Green </COLOR>
    </COLORS>
    <FEATURES> 
        <FEATURE> Round head </FEATURE>
        <FEATURE> Crown on head </FEATURE>
        <FEATURE> Tall tail fin </FEATURE>
    </FEATURES>
    <TAGS> 
        <TAG> REEF-FISH </TAG>
        <TAG> MULTICOLORED </TAG>
    </TAGS>
    <STATUS> ENDANGERED </STATUS>
    <DESCRIPTION> This fish is found in reefs and is common throughout Bermuda...</DESCRIPTION>
    <FISHINGLEGAL> FALSE </FISHINGLEGAL> 
    <DIET> 
        <DIETITEM> Algae </DIETITEM>
        <DIETITEM> Sea Plants </DIETITEM>
    </DIET>
    <EDIBLE> FALSE </EDIBLE> 
    <SCS-NAME> Holacanthus ciliaris </SCS-NAME>
</FISH>