class Restforce::Concerns::Picklists::PicklistValues

def valid?(picklist_entry)

cribesobjects_describesobjectresult.htm
See http://www.salesforce.com/us/developer/docs/api/Content/sforce_api_calls_des

Returns true if the picklist entry is valid for the controlling picklist. 
def valid?(picklist_entry)
  valid_for = picklist_entry['validFor'].ljust(16, 'A').unpack1('m').
              unpack('C*')
  (valid_for[index >> 3] & (0x80 >> (index % 8))).positive?
end