Github user afs commented on the issue:
https://github.com/apache/jena/pull/262
`SystemARQ.ValueExtensions` is a very old flag (that I'd complete forgotten
about!) that will make ARQ only deal with the minimum set of datatypes in
SPARQL, so no xsd:date, xsd:g*, language tags, and others appearing in the
built-in operators for "same value" and "compare".
Looking at it, the treatment I can see that the list isn't right - I'll
push a fix as part of this PR and tidy up some comments.
It is enabled in "strict mode", which is only useful for investigating
specs, and is unlikely to be perfect so check the query and results to confirm.
The set of "value spaces" is more detailed than that in XDM (XQuery and
XPath Data Model) - xsd:date and xsd:dateTimes can be compared using special
rules, duration needed a java fix, so {{NodeValue.compare}} has several special
cases.
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