In XPath 4.0 this definition is extended and the following expression
is evaluated successfully:

B B concat(for $i in 1 to 3 return $i)

and produces the expected result using BaseX v.11:

123

'C:\Program Files\Saxonica\SaxonCS-12.4\SaxonCS.exe' query -qversion:4.0
-qs:"concat(1 to 10)"
<?xml version="1.0" encoding="UTF-8"?>12345678910