Can't got attribute values or just got Error XQDY0025 in xQuery

I got nothing or "Error XQDY0025" when I use a xQuery, which is as below, but the eXide shows "Found 4 in 0.004s", please help me, can't find the problem.

for $s in doc("customers.xml")/customers/Customer 
return $s/@Name

to query the "Name" attributes in the below xml document

<customers>
<Customer Name="c2">
    <Order OrderNumber="o1">
        <Item Description="ab"> 
    i1
    </Item>
    </Order>
</Customer>
<Customer Name="c3">
    <Order OrderNumber="o2">
        <Item Description="cd"> 
    i2
    </Item>
        <Item Description="ef"> 
    i3
    </Item>
    </Order>
    <Order OrderNumber="o2">
        <Item Description="cfg"> 
    i5
    </Item>
    </Order>
</Customer>
<Customer Name="c1">
    <Order OrderNumber="o1">
        <Item Description="abc"> 
    i1
    </Item>
        <Item Description="def"> 
    i2
    </Item>
    </Order>
</Customer>
<Customer Name="c4">
    <Order OrderNumber="o1">
        <Item Description="abc"> 
    i1
    </Item>
    </Order>
    <Order OrderNumber="o2">
        <Item Description="def"> 
    i2
    </Item>
    </Order>
</Customer>