...and the GWTShell executes your *Java* code, so the regexps have to
be Java-regexp-compatible for your app to work in Hosted Mode.
In a few words:
- if you use JavaScript-only regexp constructs, your app will fail in
Hosted Mode, so developping and debugging will become a pain
- if you use Java-only regexp constructs, your app will run in Hosted
Mode but will fail in "web mode"
So you should base your developments on the JavaScript regexp syntax;
and if it fails in Hosted Mode, then find an alternate that's still
JavaScript-compaible and happens to also be Java-compatible. If you
base your devs on the Java regexp syntax, you'll only notice the
incompatibilities when testing in web mode, which generally happen
late in the development process...