The ongoing efforts of moving PHP from flex to re2c made us add a few more features. Most prominently the new switch -F which allows to accept a good part of the flex syntax for regular expressions. Using that flag even flex style definitions that have neither a '=' sign nor a ';' at the end work. There also is the new -r switch that allows to reuse a scanner definition. That way you can use the same scanner definition with different character types, different input or different output mechanisms.
Last but not least Nuno Lopes added the -D switch that allows to output a dot file that can then be visualized using graphviz tools (http://www.graphviz.org/).