OK, I found an answer myself. Not why my code behaves like this, but how 
to get it do what what I want.
Obviously, the SelectSingleNode method doesn't follow the reverse axis, 
but SelectNodes does.

Set Nodes2 = 
Node1.SelectNodes("ancestor-or-self::*[@xml:lang][1]/@xml:lang")
If Not(Nodes2.Length = 0) Then
	Response.Write "Lang:" & Nodes2(0).Text
	Response.Write " (inherited from " & 
Nodes2(0).SelectSingleNode("..").NodeName & ")"
End If

Strange enough though.

F


Francesca Baslen was caught writing:
> Hello,
> 
> Suppose I want to write a custom function which for a given node Node1 
> retrieves its language value (given by an xml:lang attribute).
> This value can be inherited -- in which case the significant language 
> value should be that of the closest ancestor which explicitly states a 
> language value.
> 
> Please take a look at my example ASP code below:
> 
> 
> <%@ LANGUAGE = "VBScript" %>
> <% Response.Buffer = True %>
> <%
> Dim XML1,XMLDoc1,Node1,Node2
> Set XMLDoc1 = Server.CreateObject("MSXML2.DOMDocument")
> XMLDoc1.setProperty "SelectionLanguage","XPath"
> XMLDoc1.Async = False
> 
> XML1 = XML1 & "<doc xml:lang=""de"">"
> XML1 = XML1 & "<block xml:lang=""en"">"
> XML1 = XML1 & "<item>Item</item>"
> XML1 = XML1 & "</block>"
> XML1 = XML1 & "</doc>"
> 
> XMLDoc1.LoadXML(XML1)
> 
> Set Node1 = XMLDoc1.SelectSingleNode("//item")
> Set Node2 = Node1.SelectSingleNode("ancestor-or-self::node()/@xml:lang")
> 
> If Not(Node2 Is Nothing) Then
>     Response.Write "Lang:" & Node2.Text
>     Response.Write " (inherited from " & 
> Node2.SelectSingleNode("..").NodeName & ")"
> End If
> 
> Set Node1 = Nothing
> Set Node2 = Nothing
> Set XMLDoc1 = Nothing
> %>
> 
> On this example, the XML document is made up of 3 nested nodes "doc", 
> "block", "item". "doc" and "block" have different xml:lang values.
> I want to test the language value of the node "doc" (Node1)
> In my understanding, the XPath expression 
> "ancestor-or-self::node()/@xml:lang" applied to Node1 is the correct 
> one. As an argument of the XML DOM SelectSingleNodemethod, it *should* 
> select the first node on the reverse axis, ie the @xml:lang of the 
> "block" node.
> 
> Problem: instead of the expected behaviour, it selects the @xml:lang of 
> the "doc" node (indeed the first node, but in the document order, *not* 
> the reverse order going from "item" upwards), and I don't understand why.
> 
> Could somebody explain this behaviour and help me solve this problem.
> 
> Thanks,
> 
> F
>