The reason Jay couldn't use that is that for some arrangements of
parameters this would lead to attributes being added after child
elements have already been added to the da:Positive element, which is
an error in XSLT.

For example, with the input specified:

<test type="positive" name="Test 1">
 <param name="p1">123</param>
 <param name="date1">July 9</param>
 <param name="p2">false</param>
</test>

Your code is equivalent to:

<da:Positive name="@name"> <!-- [sic -- forgot {}s] -->

 <xsl:attribute name="p1">123</xsl:attribute>
 <xsl:element name="da:Date">
   <xsl:attribute name="number">1</xsl:attribute>
 </xsl:element>
 <xsl:attribute name="p2">false</xsl:attribute>
</da:Positive>

Processors that don't halt when they encounter an attribute being
added after element content ignore the attribute, so either you get an
error or erroneous output; either way it's not much good.