XQuery functions do not convert their return value to the desired return type

[ThomasGravekamp]

XQuery function should convert the return value of a function to the desired return type as stated in 3.1.5.2 Function Conversion Rules of the XQuery spec.

This can be observed with the following XQuery module:

declare %public function local:test ($node as node()) as xs:string {
	if ($node instance of text()) then
    	$node
    else
    	string($node)
};

let $nodes := //tip | //tip/text()
return $nodes/local:test(.)

In goes a mixed sequence of text() and element() nodes. Only the element nodes are cast explicitly to an xs:string, text nodes are returned as is. Then, the "/" operator starts complaining:

Error: XPTY0018: The path operator should either return nodes or non-nodes. Mixed sequences are not allowed.

Playground example