function makeToken(value, positions) {
        positions = positions || [];

        return {
            value: value,
            positions: positions
        };
    }
Create a hint token with name value that occurs at the given list of
positions.

@param {string} value - name of the new hint token
@param {?Array.<number>=} positions - optional list of positions at which
     the token occurs
@return {Object} - a new hint token