In Saxon-SA, when the "=" operator (GeneralComparison)
is used to compare two sequences that contain a mixture
of untypedAtomic values together with other non-string
types, an error may be reported saying that a value of
the non-string type cannot be compared to a string.
This occurs when the first item in each sequence is
untypedAtomic, and a subsequent item in at least one of
the sequences is neither untypedAtomic nor string.
Test cases: K-GenCompEq-9|10 in XQTS