> For the complete documentation index, see [llms.txt](https://jaywin.gitbook.io/leetcode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://jaywin.gitbook.io/leetcode/solutions/0591-tag-validator.md).

# 0591. Tag Validator

<https://leetcode.com/problems/tag-validator>

## Description

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_NAME>TAG_CONTENT</TAG_NAME>`. Among them, `<TAG_NAME>` is the start tag, and `</TAG_NAME>` 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).
7. The cdata has the following format : `<![CDATA[CDATA_CONTENT]]>`. The range of `CDATA_CONTENT` is defined as the characters between `<![CDATA[` and the **first subsequent** `]]>`.
8. `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 = "<DIV>This is the first line <![CDATA[<div>]]></DIV>"
**Output:** true
**Explanation:** 
The code is wrapped in a closed tag : <DIV> and </DIV>. 
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 = "<DIV>>>  ![cdata[]] <![CDATA[<div>]>]]>]]>>]</DIV>"
**Output:** true
**Explanation:**
We first separate the code into : start\_tag|tag\_content|end\_tag.
start\_tag -> **"<DIV>"**
end\_tag -> **"</DIV>"**
tag\_content could also be separated into : text1|cdata|text2.
text1 -> **">> ![cdata[]] "**
cdata -> **"<![CDATA[<div>]>]]>"**, where the CDATA\_CONTENT is **"<div>]>"**
text2 -> **"]]>>]"**
The reason why start\_tag is NOT **"<DIV>>>"** is because of the rule 6.
The reason why cdata is NOT **"<![CDATA[<div>]>]]>]]>"** is because of the rule 7.
```

**Example 3:**

```
**Input:** code = "<A>  <B> </A>   </B>"
**Output:** false
**Explanation:** Unbalanced. If "<A>" is closed, then "<B>" must be unmatched, and vice versa.
```

**Example 4:**

```
**Input:** code = "<DIV>  div tag is not closed  <DIV>"
**Output:** false
```

**Constraints:**

* `1 <= code.length <= 500`
* `code` consists of English letters, digits, `'<'`, `'>'`, `'/'`, `'!'`, `'['`, `']'`, `'.'`, and `' '`.

## ac

```java
```


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://jaywin.gitbook.io/leetcode/solutions/0591-tag-validator.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.