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+# Structured Document Parser
+
+A PHP library for turning semi-structured text into a tree you can work with. It gives you the pieces for each stage and leaves the grammar to you:
+
+- **Lexing.** A `Lexer` runs your matchers against the text and produces a `TokenStream`. Matchers are grouped into states, and a matcher's callback can push or pop states. Lookahead matches that consume nothing are allowed when they switch state. Each token records its line and column.
+- **Parsing.** You implement `ParserInterface` to turn tokens into a tree of your own node classes, built on `AbstractNode`. A node holds attributes, and a series of child nodes (such as a document's blocks) goes in an array attribute.
+- **Transforming.** A `NodeTraverser` walks the tree and calls your `NodeVisitorInterface` visitors, which can replace or remove nodes.
+- **Rendering.** `VisitorInterface`, `VisitableInterface` and `RendererInterface` are extension points for double-dispatch visitors, for example a renderer with a `visitHeading()` method per node type.
+
+## Requirements
+
+PHP 8.2 or later with the `mbstring` extension.
+
+## Installation
+
+```sh
+composer require chrisjenkinson/structured-document-parser
+```
+
+## Usage
+
+This example parses a small Markdown-like document with headings and paragraphs, then gives each heading an id.
+
+```php
+require __DIR__ . '/vendor/autoload.php';
+
+use chrisjenkinson\StructuredDocumentParser\Finder\RegexFinder;
+use chrisjenkinson\StructuredDocumentParser\Lexer\Lexer;
+use chrisjenkinson\StructuredDocumentParser\Matcher\AbstractMatcher;
+use chrisjenkinson\StructuredDocumentParser\Matcher\MatchedText;
+use chrisjenkinson\StructuredDocumentParser\Node\AbstractNode;
+use chrisjenkinson\StructuredDocumentParser\Node\NodeInterface;
+use chrisjenkinson\StructuredDocumentParser\NodeTraverser\NodeTraverser;
+use chrisjenkinson\StructuredDocumentParser\NodeVisitor\AbstractNodeVisitor;
+use chrisjenkinson\StructuredDocumentParser\Parser\ParserInterface;
+use chrisjenkinson\StructuredDocumentParser\State\InitialState;
+use chrisjenkinson\StructuredDocumentParser\Token\TokenStream;
+
+// 1. Matchers recognise pieces of text. The token type is the matcher name without "Matcher".
+final class RegexMatcher extends AbstractMatcher
+{
+    private readonly RegexFinder $finder;
+
+    public function __construct(private readonly string $type, string $pattern)
+    {
+        $this->finder = new RegexFinder($pattern);
+    }
+
+    public function getName(): string
+    {
+        return $this->type . 'Matcher';
+    }
+
+    public function match(string $text): ?MatchedText
+    {
+        if (!$this->finder->find($text)) {
+            return null;
+        }
+
+        return new MatchedText($this->finder->getMatches(['all', 'level', 'text']));
+    }
+}
+
+// 2. A state holds the matchers that apply at a point in the document.
+$state = new InitialState();
+$state->registerMatcher(new RegexMatcher('Heading', '/(?<all>(?<level>#{1,6}) (?<text>[^\n]*)\n?)/A'));
+$state->registerMatcher(new RegexMatcher('Paragraph', '/(?<all>(?<text>[^#\n][^\n]*)\n?)/A'));
+$state->registerMatcher(new RegexMatcher('BlankLine', '/(?<all>\n)/A'));
+
+$tokens = (new Lexer($state))->tokenise("# Title\nSome text.\n\n## Section\nMore text.\n");
+
+echo $tokens, "\n\n";
+
+// 3. Your own node classes and parser turn tokens into a tree.
+final class Document extends AbstractNode {}
+final class Heading extends AbstractNode {}
+final class Paragraph extends AbstractNode {}
+
+final class DocumentParser implements ParserInterface
+{
+    public function parse(TokenStream $tokens): NodeInterface
+    {
+        $blocks = [];
+
+        while (null !== $token = $tokens->getCurrentToken()) {
+            $tokens->consumeToken();
+
+            $block = match ($token->getType()) {
+                'Heading'   => new Heading(),
+                'Paragraph' => new Paragraph(),
+                default     => null,
+            };
+
+            if (null === $block) {
+                continue;
+            }
+
+            $block->setAttribute('text', $token->getValue('text'));
+
+            if ($token->hasKey('level')) {
+                $block->setAttribute('level', mb_strlen($token->getValue('level')));
+            }
+
+            $blocks[] = $block;
+        }
+
+        $document = new Document();
+        $document->setAttribute('blocks', $blocks);
+
+        return $document;
+    }
+}
+
+$document = (new DocumentParser())->parse($tokens);
+
+// 4. Visitors transform the tree: here, giving each heading an id.
+final class HeadingIdVisitor extends AbstractNodeVisitor
+{
+    public function enterNode(NodeInterface $node): ?NodeInterface
+    {
+        if ($node instanceof Heading) {
+            $node->setAttribute('id', mb_strtolower(str_replace(' ', '-', $node->getAttribute('text'))));
+        }
+
+        return null;
+    }
+}
+
+$traverser = new NodeTraverser();
+$traverser->addVisitor(new HeadingIdVisitor());
+
+echo $traverser->traverse($document), "\n";
+```
+
+The lexer produces these tokens:
+
+```
+Heading (# Title)
+Paragraph (Some text.)
+BlankLine ()
+Heading (## Section)
+Paragraph (More text.)
+```
+
+and the traversed document contains the headings with their ids:
+
+```json
+{
+    "attributes": {
+        "blocks": [
+            {
+                "attributes": {
+                    "text": "Title",
+                    "level": 1,
+                    "id": "title"
+                },
+                "nodes": []
+            },
+            ...
+        ]
+    },
+    "nodes": []
+}
+```
+
+If no matcher matches, or more than one does, the lexer throws `NoTokenFoundException` or `AmbiguousTokenFoundException`, with the line, column and the text at that point.
+
+## Development
+
+```sh
+composer install
+composer test     # phpspec, PHPUnit, PHPStan and the code style check
+composer cs-fix   # fix code style
+```
+
+## Licence
+
+GPL-3.0-or-later. See [LICENSE](LICENSE).
diff --git a/composer.json b/composer.json
index 05a8d76..395d42e 100644
--- a/composer.json
+++ b/composer.json
@@ -15,7 +15,7 @@
     "jangregor/phpstan-prophecy": "1.0.*",
     "friendsofphp/php-cs-fixer": "3.95.*"
   },
-  "license": "MIT",
+  "license": "GPL-3.0-or-later",
   "authors": [
     {
       "name": "Chris Jenkinson",