[xsl] Convert paramter to a sequence

[andrew welch <andrew.j.welch@xxxxxxxxx>]

(following on from todays sudoku task) how do you go about converting
a parameter into a sequence of integers?

So:

<xsl:variable name="board" select="('1, 2, 3')" as="xs:integer+"/>

becomes:

<xsl:param name="board" .... as="xs:integer+"/>

But this fails as the passed in value is typed as a String.  How do
you get from the String "1, 2, 3" to the typed sequence (1, 2, 3) ?

thanks
andrew