#From http://ruby-doc.org/core-1.9.3/Regexp.html

/[a-w&&[^c-g]z]/ # ([a-w] AND ([^c-g] OR z))
# This is equivalent to:
/[abh-w]/

# but running this via irb gives:
>> /[a-w&&[^c-g]z]/
(irb):60: warning: character class has `[' without escape
(irb):60: warning: regexp has `]' without escape

# but seems ok via rubular.com. Why?!!