[xsl] Is the user-defined sort function in the FO31 spec providing any feature the fn:sort does not provide?

["Martin Honnen martin.honnen@xxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

I wonder whether https://www.w3.org/TR/xpath-functions-31/#sorting which 
defines an "example function" that "takes two arguments, a sequence to 
be sorted, and a function to compute a sort key" is needed in the spec 
that defines https://www.w3.org/TR/xpath-functions-31/#func-sort which 
"Sorts a supplied sequence, based on the value of a sort key supplied as 
a function".

It seems like the example is not providing any additional feature to the 
now XPath built-in fn:sort.