Given a string representing a code snippet, you need to 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: The code must be wrapped in a valid closed tag. Otherwise, the code is invalid. 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. A valid TAG_NAME only contain upper-case letters, and has length in range [1,9]. Otherwise, the TAG_NAME is invalid. 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. 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. 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 : <![CDATA[CDATA_CONTENT]]>. The range of CDATA_CONTENT is defined as the characters between <![CDATA[ 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. Valid Code Examples: Input: "<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 unmatched start tag with invalid TAG_NAME, it should be considered as plain text, not parsed as tag. So TAG_CONTENT is valid, and then the code is valid. Thus return true. Input: "<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. Invalid Code Examples: Input: "<A> <B> </A> </B>" Output: False Explanation: Unbalanced. If "<A>" is closed, then "<B>" must be unmatched, and vice versa. Input: "<DIV> div tag is not closed <DIV>" Output: False Input: "<DIV> unmatched < </DIV>" Output: False Input: "<DIV> closed tags with invalid tag name <b>123</b> </DIV>" Output: False Input: "<DIV> unmatched tags with invalid tag name </1234567890> and <CDATA[[]]> </DIV>" Output: False Input: "<DIV> unmatched start tag <B> and unmatched end tag </C> </DIV>" Output: False Note: For simplicity, you could assume the input code (including the any characters mentioned above) only contain letters, digits, '<','>','/','!','[',']' and ' '.