'Set dictionary item.
Args:
key: Key of new item.  Key is case insensitive, so "d[\'Key\'] = value "
will replace previous values set by "d[\'key\'] = old_value".
item: Item to store.'

def __setitem__(self, key, item):

    caseless_key = key.lower()
    if (caseless_key in self.caseless_keys):
        del self.data[self.caseless_keys[caseless_key]]
    self.caseless_keys[caseless_key] = key
    self.data[key] = item
