Date

From Rails, or more specifically, ActiveSupport's json.rb:

# When +true+, Hash#to_json will omit quoting string or symbol keys
# if the keys are valid JavaScript identifiers.  Note that this is
# technically improper JSON (all object keys must be quoted), so if
# you need strict JSON compliance, set this option to +false+.
mattr_accessor :unquote_hash_key_identifiers
@@unquote_hash_key_identifiers = true