[xsl] Casting single-item sequences to atomic values

[Christian Roth <roth@xxxxxxxxxxxxxx>]

Hi,

why is

  (1) cast as xs:integer == 1

Or is it?

I hit upon this while trying to understand why this works:

  subsequence( ('a','b'), (1), 1)

subsequence() expects an xs:double as its second parameter, but not a
single-item _sequence_ of xs:double's. Because it works, "(1) cast as
xs:double" must be equivalent to "1 cast as xs:double", and therefore "(1) =
1".

Why I got that much confused is my following thinking on the description of
"cast" at <http://www.w3.org/TR/xpath20/#id-cast>.

It says:

> 1. Atomization is performed on the input expression.

With fn:data( (1) ) returning the sequence of atomized values of each of its
input sequence's members, this IMO yields (1).

> 2. If the result of atomization is a sequence of more than one atomic
value

Does not apply.

> 3. If the result of atomization is an empty sequence: 

Does not apply.

> 4. If the result of atomization is a single atomic value

Also does not apply in my thinking, as I get a _sequence_ of a single atomic
value. There's no step that tackles the case where the result of atomization
is a sequence of a single atomic value.

Therefore, I guess that a single-atomic-valued-item sequence is the same (or
equivalent?) as its single atomic member. I vaguely remember reading that long
time ago somewhere in the spec, but cannot find it now. Can someone please
point me to the relevant section? Thanks!

Regards
Christian