OCaml HTML5 parser/serialiser based on Python's JustHTML
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README.md
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README.md
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# html5rw - Pure OCaml HTML5 Parser
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# html5rw - Pure OCaml HTML5 Parser and Conformance Checker
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A pure OCaml HTML5 parser implementing the WHATWG HTML5 parsing specification.
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A pure OCaml HTML5 parser and validator implementing the WHATWG HTML5 specification.
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This library passes the html5lib-tests suite and provides full support for
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tokenization, tree construction, encoding detection, and CSS selector queries.
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tokenization, tree construction, encoding detection, CSS selector queries, and
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conformance checking.
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This library was ported from [JustHTML](https://github.com/EmilStenstrom/justhtml/).
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## Key Features
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- **WHATWG Compliant**: Implements the full HTML5 parsing algorithm with proper error recovery
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- **Conformance Checker**: Validates HTML5 documents against the WHATWG specification
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- **CSS Selectors**: Query the DOM using standard CSS selector syntax
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- **Streaming I/O**: Uses bytesrw for efficient streaming input/output
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- **Encoding Detection**: Automatic character encoding detection following the WHATWG algorithm
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- **Entity Decoding**: Complete HTML5 named character reference support
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- **Multiple Output Formats**: Text, JSON (Nu validator compatible), and GNU-style output
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## Libraries
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- `html5rw` - Core HTML5 parser
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- `html5rw.check` - Conformance checker library
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## Command Line Tool
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The `html5check` CLI validates HTML5 documents:
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```bash
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# Validate a file
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html5check index.html
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# Validate from stdin
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cat page.html | html5check -
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# JSON output (Nu validator compatible)
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html5check --format=json page.html
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# GNU-style output for IDE integration
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html5check --format=gnu page.html
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# Show only errors (suppress warnings)
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html5check --errors-only page.html
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# Quiet mode - show only counts
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html5check --quiet page.html
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```
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Exit codes: 0 = valid, 1 = validation errors, 2 = I/O error.
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## Usage
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### Parsing HTML
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```ocaml
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open Bytesrw
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let reader = Bytes.Reader.of_string "<p>Fragment content</p>"
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let doc = Html5rw.parse ~fragment_context:ctx reader
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```
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### Validating HTML
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```ocaml
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open Bytesrw
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(* Check HTML from a string *)
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let html = "<html><body><p>Hello</p></body></html>"
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let reader = Bytes.Reader.of_string html
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let result = Htmlrw_check.check reader
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(* Check for errors *)
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if Htmlrw_check.has_errors result then
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print_endline "Document has errors";
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(* Get all messages *)
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let messages = Htmlrw_check.messages result in
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List.iter (fun msg ->
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Format.printf "%a@." Htmlrw_check.pp_message msg
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) messages;
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(* Get formatted output *)
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let text_output = Htmlrw_check.to_text result in
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let json_output = Htmlrw_check.to_json result in
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let gnu_output = Htmlrw_check.to_gnu result
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```
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The checker validates:
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- Parse errors (malformed HTML syntax)
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- Content model violations (invalid element nesting)
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- Attribute errors (invalid or missing required attributes)
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- Structural issues (other conformance problems)
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## Installation
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