Using Pegs in Janet

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Janet uses parser expression grammars (PEGs) instead of regular expressions.
PEGs in Janet are defined using associative data structures with named rules.
Rules can refer to other rules, including recursively, and can run arbitrary functions.
A simplified HTML subset can be parsed using sequences, choices, captures, and back-references.
The :main rule is the starting point for parsing in Janet.
Rules like :tagged, :open-tag, :close-tag, and :value are defined to parse HTML tags and content.
Match-time captures (cmt) and back-references are used to ensure tag names match in opening and closing tags.
The :value rule handles nested tags and untagged content using the any and + combinators.
The :untagged rule matches characters that are not part of a tag.
Captures can be structured into data using replace and struct functions.
PEGs can be compiled for better performance using peg/compile.
Example usage shows parsing HTML strings into structured data.

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