Could the second argument $index be renamed to $position, 

    array:get($array as array(*), $index as xs:integer) as item()*

to match other function signatures

    array:remove($array as array(*), $position as xs:integer) as array(*)
amd
    array:insert-before($array	 as array(*), $position	 as xs:integer, $member	 as item()*) as array(*)


Similarly, the first argument of

array:sort($input as array(*)) as array(*)
array:sort($input	 as array(*), $key	 as function(item()*) as xs:anyAtomicType*) as array(*)
array:flatten($input as item()*) as item()*

be renamed to $array, matching the rest of the "array" functions.

While these are trivial changes, it might be beneficial for IDE users.