RE: Possible to pass 'empty sequence' to function?

> When is it a good idea to type a variable/param as "xs:string?" - what
> benefits does it bring over not specifying the "as" attribute?  
> 

I think it's always a good idea to declare the data types of your
parameters: it documents the assumptions that the writer of a function or
template is making about the way it will be called, it catches many
programming errors (such as supplying an empty sequence to a function that
wasn't written to expect one), and it gives the optimizer more information
to work with.

Michael Kay
http://www.saxonica.com/