Constructor functions & `cast as` -- why both?

Hi,

According to the XPath specifications are constructor functions and the cast 
expression defined to be semantically equivalent. I wonder, why then provide 
both?

Here my speculation:

* The two uses different default namespaces. Hence, it can be practical on the 
stylesheet-writing level. But this aspect is not more than convenience, 
right?

* A usability aspect of the language. One might argue that multiple ways of 
expressing the same thing allows users to choose their way which fits them 
the best(a psychological aspect). _For example_, the `cast as` expression can 
be percepted as changing the type of an existing value, while a constructor 
function can be percepted as creating a new value.

What was the reasoning for creating the two?

Also, does anyone have any particular opinions/experience about the two?


Cheers,

		Frans