Saxon

Using the attached XSLT 4.0 - with extensions enabled - with SaxonJ 12.0 PE:

When running the attached XSLT (test.xsl) from the command-line against itself I get the following error:

Error in xsl:variable/@select on line 9 column 76 of test.xsl:
  XPTY0004  The required item type of the second argument of fn:slice() is map(*)
Errors were reported during stylesheet compilation

Further tests showed that fn:slice must have 2 arguments: item()* and map(*) - the Saxon 12 documentation (and the spec) however indicate 4 arguments can be supplied - with the last 3 optional: 

fn:slice($input as item()*, $start as xs:integer?, $end as xs:integer?, $step as xs:integer?) as item()*