I would like to know if there is a quick way with xslt to check if an element in a xml document is at a valid position in the element tree structure defined in the xsd schema?

Not really.

With a schema-aware stylesheet in XSLT 2.0 you can validate a document (or any subtree) against a schema, but the effect is a fatal error if the document is invalid, which doesn't seem to be what you are looking for.

Perhaps you could explain the background to the requirement.

Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference

I want to test the hierarchy of all elements in the xml tree in a non schema aware processor.
I can check it with an external document (doctree.xml)with all the paths in it(generated from the xsd) so I could test the path as stringvalue for every element

I build the path string with the expression
concat('//',string-join(for $i in (ancestor-or-self::node()[name()]) return $i/local-name(),'/'))

I now can search the elementtree in the xml like:
select="if doc('doctree.xml')//path[.= concat('//',string-join(for $i in (ancestor-or-self::node()[name()]) return $i/local-name(),'/'))])"

but this seems to be a bit too complicated to me

You need to explain the requirement more clearly.

You have a set of possible paths in some file doctree.xml, yes? And you now want to test whether one of these paths matches some other document, say instance.xml?

Your proposed expression if doc('doctree.xml')//path[.= concat('//',string-join(for $i in (ancestor-or-self::node()[name()]) return $i/local-name(),'/'))]) works entirely within a single document, so it's not clear what it's trying to achieve.

Do you want to know whether all the paths in doctree have a match, or whether a specific one does, or whether a particular node in instance.xml matches one of the paths, or what???

Instead of generating a data file containing paths, why not generate an XSLT stylesheet or XQuery that gives you the answer directly?

Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference

Yes I want to test if a path of a particular node in instance.xml matches the value of a <path> element in paths.xml

like this:
instance.xml
<elementA><elementB>Value of B</elementB></elementA>

paths.xml
<paths>
    <path>//elementA</path>
    <path>//elementA/elementB</path>
</paths>
when I want to test element B I'll test the string value "//elementA/ElementB"
when I find this value in the paths.xml//paths/path its OK

I'd suggest that instead of generating paths.xml as data, you generate

<xsl:template match="//elementA" mode="test"/>
<xsl:template match="//elementA/elementB" mode="test"/>
<xsl:template match="*" mode="test">NO MATCH</xsl:template>

and import this into your stylesheet. You can then test element B as

<xsl:variable name="x">
  <xsl:apply-templates mode="test"/>
</xsl:variable>
<xsl:if test="$x = 'NO MATCH'">...

Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference

Great, thanx this is what helps me a lot. I already had tried it with the * path description but I didn't use it in combination with mode and variable. Now only hoping I don't have recursive elements