The current hierarchy is:
+=for comment
+This tree is generated by regen/warnings.pl. Any changes made here
+will be lost.
+
+=for warnings.pl begin
+
all -+
|
+- closure
+- experimental --+
| |
| +- experimental::lexical_subs
+ | |
+ | +- experimental::lexical_topic
+ | |
+ | +- experimental::regex_sets
+ | |
+ | +- experimental::smartmatch
|
+- glob
|
|
+- void
+=for warnings.pl end
+
Just like the "strict" pragma any of these categories can be combined
use warnings qw(void redefine);