- test files:
   http://www.dbis.informatik.uni-goettingen.de/Mondial/mondial.xml
   https://www.ibiblio.org/xml/examples/shakespeare/hamlet.xml 

- call saxon with hamlet.xml as context document

for $x in //PERSONA
where some $l in /PLAY//LINE satisfies contains($l,$x)
return $x

(all person names in the "Hamlet" play that are mentioned in some line of it)
=> 1 result: Guildenstern

-- shows that paths accessing the context document are allowed in the where-clause.

For the following, again called with hamlet.xml as context document,
saxon (9.8.0.7 downloaded 19.1.2018, both HE and EE) throws an error:

All country names in "Mondial" that are mentioned in some line of "Hamlet":

for $x in doc("file:mondial.xml")//country/name
where some $l in /PLAY//LINE satisfies contains($l,$x)
return $x

==>
may@login:~/teaching/ssd/XQuery$ saxonXQ -s:hamlet.xml hamletmondialbug.xq
Exception in thread "main" java.lang.StackOverflowError
        at net.sf.saxon.expr.Expression.computeDependencies(Expression.java:1231)
        at net.sf.saxon.expr.Expression.computeStaticProperties(Expression.java:1174)
        at net.sf.saxon.expr.Expression.getDependencies(Expression.java:765)
        at net.sf.saxon.expr.Expression.computeDependencies(Expression.java:1234)
        at net.sf.saxon.expr.Expression.computeStaticProperties(Expression.java:1174)
        at net.sf.saxon.expr.Expression.getDependencies(Expression.java:765)
        at net.sf.saxon.expr.Expression.computeDependencies(Expression.java:1234)
        at net.sf.saxon.expr.Assignation.computeDependencies(Assignation.java:133)
        at net.sf.saxon.expr.Expression.computeStaticProperties(Expression.java:1174)
        at net.sf.saxon.expr.Expression.getDependencies(Expression.java:765)
        at net.sf.saxon.expr.Expression.computeDependencies(Expression.java:1234)
        at net.sf.saxon.expr.Expression.computeStaticProperties(Expression.java:1174)
        at net.sf.saxon.expr.Expression.getDependencies(Expression.java:765)
        at net.sf.saxon.expr.Assignation.countReferences(Assignation.java:502)
        at net.sf.saxon.expr.Assignation.rebuildReferenceList(Assignation.java:488)
        at net.sf.saxon.expr.Assignation.verifyReferences(Assignation.java:475)
        at net.sf.saxon.expr.LetExpression.optimize(LetExpression.java:266)
        at net.sf.saxon.expr.flwor.FLWORExpression.optimize(FLWORExpression.java:572)
        at net.sf.saxon.expr.LetExpression.optimize(LetExpression.java:317)
        [... recursion...]

(aside: with saxon9he 9.7.0.8 (from Sept 2016) this worked correctly)


Note that

let $h := .
for $x in doc("file:/home/may/Mondial/Mondial-III/mondial.xml")//country/name
where some $l in $h/PLAY//LINE satisfies contains($l,$x)
return $x

works well and returns 5 results.


20.1.2018 in the morning: <a href="https://saxonica.plan.io/issues/3634">solved</a>.