Select follower tag, selectSingleNode in msxml

How can I select the MEDIUM from that xml with VBScript Msxml?

<reference_list>
    <reference_tag>VAT</reference_tag>
    <reference_value>123</reference_value>
</reference_list>
<reference_list>
    <reference_tag>PRIORITY</reference_tag>
    <reference_value>MEDIUM</reference_value>
</reference_list>

I currently selected the PRIORITY tag, but i want to the follower reference_value's value MEDIUM:

xmlDoc.selectNodes("//insert_shipment/reference_list[reference_tag ='PRIORITY']")

Looping is not an option now, I have to select just that one.