Define a key
for the property we want
to use for grouping.
Select all of the nodes . . .
This can be really complicated.
Many people don't enjoy this method.
XSLT 2.0 attempts to make grouping simpler.
For each unique grouping value . . .
Define an XPath expression . . .
Select all of the nodes . . .
This is much easier than it used to be.
Instead of dealing with each . . .