Show XML attribute value in document structure information !

I am working in a specific XML type:


<Product ID="2112570">

<Values>

<Value AttributeID="Colour">foo</Value>
<Value AttributeID="Size">foo</Value>
<MultiValue AttributeID="CODE">

<Value>8717868033539</Value>

</MultiValue>

<Value AttributeID="Description">foo</Value>

</Values>

</Product>

I designed a custom XML file type, with parser rules that work fine, except for the Document Explorer. In the Document Structure pane of the Editor, I want to show a hierarchical view:

[Product ID value]

Colour

Size

Description

In other words, I want to use the value of the Product element's ID attribute. I can easily come up with an XPath and put it in the parser rules. However, Studio doesn't take the value (e.g. 2112570), but the name of the attribute (e.g. Product ID).

I'd think this would work, but it doesn't:

I found another user on this forum who managed to do it, but I don't understand his solution: https://community.sdl.com/product-groups/translationproductivity/f/studio/8664/display-element-content-in-document-explorer-in-studio-editor

Any help would be appreciated!