[xsl] How do I determine that an item is a numeric atomic value?

["Costello, Roger L." <costello@xxxxxxxxx>]

Hi Folks,

How do I tell that an item is a numeric atomic value?

I want to create a function, f:is-number(exp), that returns true if the value
of $exp is a numeric atomic value, false otherwise.

For example, f:is-number(3.14) should return true. If it is called with an
element that contains the value 3.14 then it should return false.

How do I determine that the value of $exp is a numeric atomic value?

/Roger