The format of the "explain" output which displays a compiled and optimized expression
tree has changed. The format is now XML, making the raw output amenable to further processing,
for example filtering or graphical display. The -e flag on the Query command
line is extended to allow -explain:filename, so that the output can more easily be
captured in a file.
The options -explain and -explain:filename have been added to the Transform
command line allowing an expression tree to be generated for an entire stylesheet. The extension attribute
saxon:explain remains available for more selective reporting.
From the Java level, explain output is available via a new method on the Expression class.
The old display() method is retained (for the time being) for compatibility, but produces
output in the new format.
