This comes up a lot in the DITA stylesheets. John Lumley did a fair bit of
work on optimizing such patterns, and the basic technology is there in current
Saxon releases, but not well productized, so you have to configure it using
some pretty complex configuration files. As it happens I've just been studying
the code to see what part of it could be packaged in a more usable way for
Saxon 9.8. But in the absence of that...