For and let expressions

XPath 4.0 allows multiple let clauses, or multiple for clauses (but not a mixture) in an expression. For example:

• let $i := 2 let $j := 3 return $i + $j
• for $i in 1 to 10 for $j in 1 to 3 return $i * $j

This feature is implemented from Saxon 12.3.