Firstly, everything you talk about here was defined in XSLT 2.0, and was
unchanged in 3.0.

You've left out a crucial phrase from your quotation, which is present in both
2.0 and 3.0:

If the as attribute is specified, then the supplied value of the variable is
converted to the required type, using the function conversion rules.

Follow the link to the function conversion rules, and you'll see that they
don't allow casting from string to integer.

Michael Kay
Saxonica