Given a string representing a code snippet, implement a tag validator to parse the code and return whether it is valid.

A code snippet is valid if all the following rules hold:

1.  The code must be wrapped in a **valid closed tag**. Otherwise, the code is invalid.
2.  A **closed tag** (not necessarily valid) has exactly the following format : `TAG_CONTENT`. Among them, is the start tag, and is the end tag. The TAG\_NAME in start and end tags should be the same. A closed tag is **valid** if and only if the TAG\_NAME and TAG\_CONTENT are valid.
3.  A **valid** `TAG_NAME` only contain **upper-case letters**, and has length in range \[1,9\]. Otherwise, the `TAG_NAME` is **invalid**.
4.  A **valid** `TAG_CONTENT` may contain other **valid closed tags**, **cdata** and any characters (see note1) **EXCEPT** unmatched `<`, unmatched start and end tag, and unmatched or closed tags with invalid TAG\_NAME. Otherwise, the `TAG_CONTENT` is **invalid**.
5.  A start tag is unmatched if no end tag exists with the same TAG\_NAME, and vice versa. However, you also need to consider the issue of unbalanced when tags are nested.
6.  A `<` is unmatched if you cannot find a subsequent `>`. And when you find a `<` or ``, all the subsequent characters until the next `>` should be parsed as TAG_NAME (not necessarily valid).``
``` *   The cdata has the following format : . The range of `CDATA_CONTENT` is defined as the characters between ``and the **first subsequent** `]]>`.`` ``*   `CDATA_CONTENT` may contain **any characters**. The function of cdata is to forbid the validator to parse `CDATA_CONTENT`, so even it has some characters that can be parsed as tag (no matter valid or invalid), you should treat it as **regular characters**.`` ```

``` ``  **Example 1:**  **Input:** code =  "  This is the first line ]]>   " **Output:** true **Explanation:**  The code is wrapped in a closed tag :    and   .  The TAG_NAME is valid, the TAG_CONTENT consists of some characters and cdata.  Although CDATA_CONTENT has an unmatched start tag with invalid TAG_NAME, it should be considered as plain text, not parsed as a tag. So TAG_CONTENT is valid, and then the code is valid. Thus return true.  **Example 2:**  **Input:** code =  "  >>  ![cdata[]] ]>]]>]]>>]   " **Output:** true **Explanation:** We first separate the code into : start_tag|tag_content|end_tag. start_tag -> ** "**   **"** end_tag -> ** "**   **"** tag_content could also be separated into : text1|cdata|text2. text1 -> ** ">>  ![cdata[]]  "** cdata -> ** "]>]]> "**, where the CDATA_CONTENT is ** "**  **]> "** text2 -> ** "]]>>] "** The reason why start_tag is NOT ** "**  **>> "** is because of the rule 6. The reason why cdata is NOT ** "]>]]>]]> "** is because of the rule 7.  **Example 3:**  **Input:** code =  "    " **Output:** false **Explanation:** Unbalanced. If  " " is closed, then  " **" must be unmatched, and vice versa.**  **  **Constraints:**  *   `1 <= code.length <= 500` *   `code` consists of English letters, digits, `'<'`, `'>'`, `'/'`, `'!'`, `'['`, `']'`, `'.'`, and `' '`.  **`` ```


def is_valid(code, i):
    if i >= len(code) or code[i] != '<':
        return False, i
    i += 1
    name_start = i
    while i < len(code) and code[i].isupper():
        i += 1
    name_len = i - name_start
    if name_len < 1 or name_len > 9 or code[i] != '>':
        return False, i
    i += 1

    while i < len(code) and code[i] != '<':
        i += 1
    if i + 2 + name_len >= len(code) or code[i:i + 2 + name_len] != '</' + code[name_start:i] + '>':
        return False, i
    return True, i + 2 + name_len


def validate_code_snippet(code):
    is_valid_code, i = is_valid(code, 0)
    return is_valid_code and i == len(code)
