private void pop (char c) throws JSONException {
        if (this.top <= 0) { throw new JSONException("Nesting error."); }
        char m = this.stack[this.top - 1] == null ? 'a' : 'k';
        if (m != c) { throw new JSONException("Nesting error."); }
        this.top -= 1;
        this.mode = this.top == 0
                                 ? 'd'
                                 : this.stack[this.top - 1] == null
                                                                   ? 'a'
                                                                   : 'k';
    }