<p>
<el att='a'>x</el>
<el att='b'>x</el>
<el att='c'>x</el>
<el att='d'>y</el>
</p>
I have about 1200 lines of this, so keys are out.

Why discount keys?

Because I have so many variants on (above) x, y.
ditto on the att values, so I would have to define about 200 unique
keys.

 <xsl:key name="generic" match="el"
   use="concat(@att,':',.)"/>

Iterate over @att, group by el content, or vice versa.
What's the problem?