'One left token and one right token, normalized to lowercase'

@staticmethod
def _default_context(tokens, i):

    left = (tokens[(i - 1)].lower() if (i != 0) else u'*START*')
    right = (tokens[(i + 1)].lower() if (i != (len(tokens) - 1)) else u'*END*')
    return (left, right)
