RelationalExpr doing alpha comparisons?

[Dave]

According to Michael Kay, a relational comparison doesn't compare strings,
but converts strings to numbers if possible and compares numeric values.

When for example this element is evaluated by Xalan in my stylesheet:

<xsl:when test="//Number &gt; //HighestNumber">

where number and highest number contain numbers.

It seems to compare the two nodes as strings, so for example, 5 is
considered greater than 100.  This seems contradictory to Kay's statements.

It worked when I replaced the previous element with:

<xsl:when test="number(//Number) &gt; //HighestNumber">.

I'm just bothered that it didn't behave the way I thought it should.  Of
course I'm just a beginner at all this.  Is this a problem with Xalan,
Michael Kay, or me?

Thanks,
Dave Kaplan