What are the differences between perl and java regex capabilities?

Question

What are the differences between perl and java with regard to what regular expression terms are supported?

This question is isolated to just the regular expressions,

Answer 1

The slides from Tom Christiansen's OSCON talk Unicode Support Shootout: The Good, the Bad, & the (mostly) ugly cover some of the differences between Perl and Java (and other languages) regarding support of the Unicode technical recommendations for regexes, and they distinguish between Java 1.6 and 1.7 (which improves support significantly).